Focus detecting device having light distribution detection

ABSTRACT

There is disclosed a focus detecting device adapted for use in a camera or the like and provided with; a phototaking optical system for forming an image of the object on a reference plane; a focus detecting optical system for separating, from the light beam passing through the phototaking optical system, at least a pair of light beams passing through spatially different areas on a first predetermined plane axially spaced by a first distance from the reference plane, thereby forming images of the object; a photoelectric converting device composed of plural photosensor elements and adapted to generate object image signals corresponding to the intensity distribution of the object images formed by the focus detecting optical system; a phototaking optical system information device for generating information on the shape of exit pupil at fully-open diaphragm of the phototaking optical system and on a second distance from the reference plane to the exit pupil; a focus detecting optical system information device for generating information on the form of the areas on the first predetermined plane and on the first distance; a light amount distribution detecting device for determining the decrease in light amount on the plane of photo sensor elements of the photoelectric converting device as light amount information relating to the position on the plane of photosensor elements, encountered when the phototaking optical system and the focus detecting optical system are combined, based on the information from the phototaking optical system information device and from the focus detecting optical system information device; and a focus detection calculation device for effecting a process on the object image signals based on the light amount distribution information, thereby determining the defocus amount of the current object image plane relative to the reference plane.

This is a division of application Ser. No. 08/311,896 filed Sep. 26,1994, which is a continuation of application Ser. No. 08/225,913 filedApr. 11, 1994 (abandoned), which is a continuation of application Ser.No. 08/129,576 filed Sep. 30, 1993 (abandoned), which is a continuationof application Ser. No. 08/032,176 filed Mar. 15, 1993 (abandoned),which is a continuation of application Ser. No. 07/951,317 filed Sep.25, 1992 (abandoned), which is a continuation of application Ser. No.07/837,106 filed Feb. 18, 1992 (abandoned), which is a continuation ofapplication Ser. No. 07/641,431 filed Jan. 15, 1991 (abandoned).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a focus detecting device for use in acamera or the like.

2. Related Background Art

There is already known a focus detecting device disclosed in the U.S.patent application Ser. No. 457,408 filed Dec. 26, 1989 by the presentapplicant. Said device is based on a principle of forming a pair ofimages of an object on a photoelectric converting device from a pair oflight beams passing through a phototaking optical system by means of afocus detecting optical system of so-called split pupil type, obtainingimage signals of said object by photoelectric conversion of said imagesby said photoelectric converting device, and effecting a predeterminedcalculation on said image signals thereby determining the defocus amountof the phototaking optical system.

However, in such focus detecting device of split pupil system, a certaincombination of the phototaking optical system and the focus detectingoptical system gives rise to a vignetting of the light beams used forfocus detection, and, such vignetting, if not uniform, undesirablyaffects the precision of focus detection and may render the focusdetecting operation totally impossible in the worst case.

In the following there will be explained the cause of such vignetting,with reference to FIG. 1.

FIG. 1 illustrates a focus detecting optical system of so-called splitpupil system, disclosed in the U.S. patent application Ser. No. 457,408of the present applicant. Said optical system is composed of a fieldmask 300 positioned at the primary image plane of the phototakingoptical system and provided with an aperture 300A for defining the areaof focus detection in the object field, a field lend 301 positionedbehind said field mask; re-imaging lenses 303A, 303B, 303C, 303Darranged in two pairs for re-imaging the images of an object on asecondary image plane; and a diaphragm mask 302 positioned in front ofsaid re-imaging lenses and provided with four apertures 302A, 302B,302C, 302D for limiting the light beams entering said re-imaging lenses.Thus re-focused object images are respectively projected ontophotosensor units (for example CCD image sensors) 304A, 304B, 304C, 304Dof the photoelectric converting device 304 positioned at the secondaryimage plane, whereby object image signals corresponding to the lightintensity distributions of the object images are generated from saidphotosensor units.

In the above-explained structure, the forms of four apertures 302A,302B, 302C, 302D are projected by the field lens 301 onto a pupil plane305 (hereinafter also called a focus detecting pupil) positioned at apredetermined distance d0 from the primary image plane, wherein theprojected forms respectively constitute pupil areas 305A, 305B, 305C,305D (hereinafter also called focus detecting pupil diaphragms).Consequently the object images re-focused on the secondary image planeare solely formed by the light beams passing through said pupil areas305A, 305B, 305C and 305D.

FIG. 2 is a cross-sectional view, along a plane containing the X- andZ-axes, of the focus detecting optical system shown in FIG. 1.

The rays passing through the pupil area 305A or 305B and concentratedbetween end points A and C in the X-direction of the aperture 300A ofthe field mask 300 have always to pass through an area between hatchedportions (said area being defined inside lines A-F and C-H from theprimary image plane to the pupil plane 305 at a distance d0 there-from,and inside extensions of lines C-F and A-H beyond said pupil plane 305,wherein F and H are external end points in the X-direction of the pupilareas 305A, 305B). Consequently if the phototaking optical system has arelatively small F-number so that the external end points of the exitpupil thereof are positioned in the hatched portions, the light beamsused for focus detection do not cause vignetting and do not haveundesirable effect on the focus detection. However, if the F-numberbecomes larger so that the external end points of the exit pupil arepositioned in the internal area, said light beams show vignetting whichundesirably affects the focus detection.

The influence of vignetting on the focus detection depends also on thepupil position as well as the size of the exit pupil 101. For example,if the apertures 302A, 302B of the diaphragm mask 302 are shaped likecat's eyes, the pupil areas 305A, 305B on the pupil plane 305 are shapedas shown in FIG. 3. Consequently, the rays which are concentrated on allthe points of the aperture 300A of the field mask 300 and then passthrough the apertures 302A, 302B should have passed the pupil areas305A, 305B on the pupil plane 305. Thus, if the exit pupil 101 of thephototaking optical system is positioned at the pupil plane 305, therays passing through the different points of the aperture 300A andfalling onto the photoelectric converting device 304 are subjected touniform vignetting even in the presence of vignetting. Therefore thevignetting does not cause any undesirable influence but merely resultsin a uniform loss in the light intensity received by the photosensorunits of the photoelectric converting device 304.

However, in any other plane than the pupil plane 305, the rays passingthrough the different points of the aperture 300A of the field mask 300and falling onto the photoelectric converting device 304 pass throughspatially different areas. For example, light beams which areconcentrated on points A, B and C of the aperture 300A shown in FIG. 1and then pass through the aperture 302B of the diaphragm mask 302, passthrough respectively different areas 306A, 306B and 306C shown in FIG. 4on a plane at a position d1 different from that of the pupil plane 305.Consequently, in case of vignetting when the exit pupil 101 of thephototaking optical system is not positioned on the pupil plane 105, theamounts of vignetting on the light beams passing through differentpoints of the aperture 300A and falling on the photoelectric convertingdevice 304 are not uniform, thus resulting in different losses of lightintensity depending on the locations on the photosensor units of thephotoelectric converting device 304 and undesirably affecting the focusdetection.

FIGS. 5A, 5B, 5C and 5D illustrate the states of such vignetting. InFIGS. 5B, 5C and 5D, points A', B', C', D', E', A", B", C", D" and E"correspond to the points A, B, C, D and E of the aperture 300A shown inFIG. 5A after re-focusing by the lenses 303A, 303B.

FIGS. 5B and 5C show the vignetting in the image of the aperture 300Are-focused by the lenses 303A, 303B. For an object with uniformluminocity, the vignetting does not appear in an area inside the solidline (an area including the point A for the image formed by there-focusing lens 303A; and an area including the point C for the imageformed by the lens 303B), so that the amount of light is 100%. Howeverthe vignetting occurs in such a way that the amount of light is reducedto 90-100% in an area between the solid line and the broken line, and isreduced below 90% outside the broken line. When the images formed by thelenses 303A, 303B are superposed, the vignetting-free areas do notoverlap each other as shown in FIG. 5D, and exact focus detectionbecomes impossible because two images to be compared for the focusdetection do not coincide each other.

For the above-mentioned drawback, there have been proposed followingcountermeasures.

For example, in a focus detecting device disclosed in the JapaneseLaid-open Patent Sho 55-111927, the above-mentioned drawback is resolvedby the use of two focus detecting systems with different F-numbers andby selecting a focus detecting system free from the vignetting,according to the F-number of the phototaking optical system. TheF-number for focus detection is determined by the size of acircumscribed circle including the pupil areas 305A, 305B, 305C and 305Don the pupil plane 305 shown in FIG. 1 and the position d0 of said pupilplane.

Also in a focus detecting device disclosed in the U.S. Pat. No.4,687,917 of the present applicant, the above-explained drawback isresolved by detecting the vignetting state of the focus detecting lightbeams from the output status of the focus detecting photoelectricconverting device, and, in the presence of vignetting, eliminating thelow frequency components from the output of the photoelectric convertingdevice, thereby alleviating the influence of said vignetting prior tothe calculation for focus detection.

Also in a focus detecting device disclosed in the U.S. Pat. No.4,816,663 of the present applicant, the above-mentioned drawback isresolved by calculating the amount of vignetting from the F-number ofthe exit pupil of the phototaking optical system and the positionalinformation of said exit pupil, and effecting the calculation for focusdetection so as to reduce the influence of the vignetting according tothus calculated amount of vignetting.

However, such conventional focus detecting devices have been associatedwith considerable errors in the calculation of loss in the amount oflight, because the losses in peripheral light in the phototaking opticalsystem and in the focus detecting optical system are not included in theloss of light resulting from vignetting. For this reason switching offocus detecting calculation process according to the loss of lightamount cannot be conducted in exact manner. It has also been difficultto use the output of photoelectric conversion for the focus detectionafter the correction for loss of light amount, or to use a portion ofsaid output free from loss in light amount. This drawback has becomemore serious with the recent expansion of the focus detecting area withrespect to the photographing image area, as the losses in the peripherallight amount in the phototaking optical system and in the focusdetecting optical system are no longer negligible.

SUMMARY OF THE INVENTION

The object of the present invention is to prevent the deterioration inthe accuracy of focus detection resulting from the losses in theperipheral light amount in the phototaking optical system and in thefocus detecting optical system.

Referring to FIG. 6, the focus detecting device of the present inventionis provided with a phototaking optical system 1 for forming the image ofan object on a reference plane; a focus detecting optical system 2 forseparating, from the light beams passing through said phototakingoptical system 1, at least a pair of light beams passing throughspatially different areas on a first predetermined plane axially spacedby a first distance from said reference plane; a photoelectricconverting device 3 consisting of plural photosensor elements andadapted to generate object image signals corresponding to the lightintensity distribution of the image of the object, an informationgenerating device 4 for the phototaking optical system, for generatinginformation on the F-number of the exit pupil at the fully-opendiaphragm aperture of the phototaking optical system 1, a seconddistance from said reference plane to the exit pupil, and the loss inthe light amount in the peripheral area of the phototaking opticalsystem 1; an information generating device 5 for the focus detectingoptical system, for generating information on the size of said areas onsaid first predetermined plane, said first distance, and the loss in thelight amount in the peripheral area of the focus detecting opticalsystem 2; a light amount distribution detecting device 6 for determiningthe light amount distribution information representing the loss in thelight amount on the photosensor elements of the photoelectric convertingdevice 3 as a function of position on the photosensor elements,resulting from the loss in peripheral light amount and theaforementioned vignetting of the focus detecting light beams in thecombination of the phototaking optical system 1 and the focus detectingoptical system 2, based on the information supplied from saidinformation generating devices 4, 5, and a focus detecting calculatingdevice 7 for detecting the defocus amount of the current object imageplane with respect to the reference plane, by applying a processaccording to the light amount distribution information to the objectimage signals.

The above-mentioned information generating device 4 for the phototakingoptical system may be so designed to further generate information on theshape and position of the aperture portion of lens barrel (for examplelens holding ring and hood), that may further limit the phototakinglight beams in addition to the diaphragm, and such information may beutilized in the detecting device 6 for determining the light amountdistribution on the photosensor elements of the photoelectric convertingdevice 3 when the phototaking optical system 1 is combined with thefocus detecting optical system 2.

The loss in the light amount in case the phototaking optical system 1and the focus detecting optical system 2 are mutually combined iscalculated as the light amount distribution information, based on theinformation of the phototaking system and of the focus detecting system.The object image signals generated by the photoelectric convertingdevice 3 are processed according to said distribution information, andthe focus detecting calculation is conducted by the image signals aftersaid processing. Consequently, even in case the focus detecting opticalsystem 2 is combined with various phototaking optical systems 1, theoverall loss in the light amount, including the loss by the vignettingin the focus detecting light beams and the loss in peripheral lightbeams in the optical systems, can be exactly calculated.

The processing of the object image signals according to the light amountdistribution information may be, for example, elimination of an imagesignal showing significant light amount loss, correction of the imagesignals according to the light amount loss, or elimination of lowfrequency components from the image signals in case of significant lightamount loss.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view of a focus detecting opticalsystem;

FIG. 2 is a cross-sectional view, along a plane including X- and Z-axes,of the focus detecting optical system shown in FIG. 1;

FIG. 3 is a view of pupil areas formed on a pupil plane;

FIG. 4 is a view showing, on a plane at a position d1 different fromthat of the pupil plane 305, the passing areas of light beams which arerespectively concentrated on points A, B and C of the aperture 300A inFIG. 1 and then pass through the aperture 302B of the diaphragm mask302;

FIGS. 5A to 5D are views showing different states of vignetting in casethe focus detecting light beams show vignetting;

FIG. 6 is a schematic view of the structure of a focus detecting deviceof the present invention;

FIG. 7 is a block diagram of an embodiment of the focus detecting deviceof the present invention;

FIG. 8 is a chart showing information on the peripheral light amount ofa phototaking lens as a function F(d) of the distance d from the opticalaxis on the image plane;

FIG. 9 is a view showing the form of a focus detecting pupil diaphragmon a focus detecting pupil plane;

FIG. 10 is a view showing a circle formed on the exit pupil plane of thephototaking lens 11 by a light beam passing through a coordinate (x₀,y₀) of the aperture 300A and the re-focusing lens 303B;

FIGS. 11A and 11B are charts showing the behavior of the light amountdistribution information Ka (x, y);

FIG. 12 is a chart showing the range of data to be employed in thecorrelation calculation;

FIGS. 13A to 13F are flow charts showing the control sequence of focusdetecting calculation in the present embodiment;

FIGS. 14 to 16 are perspective views showing structures of the focusdetecting optical system;

FIG. 17 is a flow chart of the control sequence of a CPU for controllingthe AF detecting system;

FIG. 18 is a view showing the change in data storage areas of thememory;

FIGS. 19A to 19D are timing charts of the function of the CPU forcontrolling the AF detecting system;

FIGS. 20A and 20B are views showing two-dimensional photosensor units;

FIG. 21 is a view of a diaphragm mask;

FIGS. 22A and 22B are views showing data, on the photosensor units,usable for the calculation for focus detection;

FIG. 23 is a chart showing a method for controlling the accumulatingtime;

FIG. 24 is a chart showing a peak value PEAK and an average value AV ofthe previous object image data;

FIG. 25 is a view of a diaphragm mask;

FIG. 26 is a block diagram showing a more detailed embodiment of thefocus detecting device;

FIG. 27 is a flow chart of the control sequence of an AF calculatingCPU;

FIGS. 28A to 28D are charts showing image signals;

FIGS. 29A and 29B are views showing focus detecting areas in the imageplane;

FIGS. 30A and 30B are views showing structure of a viewing pointdetecting device;

FIG. 31 is a view of a distance ring for lens focusing;

FIG. 32 is a chart showing monitor signals in case the lens istheoretically stopped at the in-focus position by brake application at mremaining pulses in front of the in-focus position;

FIG. 33 is a chart showing the relation between the remaining pulsenumber n and the pulse interval tn;

FIG. 34 is a chart showing drive signals for an AF motor;

FIG. 35 is a flow chart of the control sequence of a lens drive controlCPU;

FIG. 36 is a flow chart of the control sequence in an AF drive mode;

FIG. 37 is a flow chart of the control sequence in a power focus mode;

FIG. 38 is a flow chart of the control sequence in a manual mode;

FIGS. 39A, 39B and 39C are views showing selection of focus detectingareas displayed in the image field;

FIGS. 40A to 40F are views showing displays indicating focus detectionstates;

FIG. 41 is a view showing the structure of a display device;

FIG. 42 is a view showing the structure of a focus detecting deviceemploying an image display device;

FIG. 43 is a view showing an embodiment of image display outside thecamera body

FIG. 44 is a block diagram of another embodiment of the focus detectingdevice of the present invention;

FIG. 45 is a perspective view of the focus detecting optical systemonly;

FIGS. 46A to 46C are views showing change in the form of a physicaldiaphragm;

FIG. 47A is a view showing the structure of photosensor units of thephotoelectric converting device;

FIGS. 47B to 47E are schematic views showing concepts of potentials ofthe photosensor unit in the photoelectric converting device; and

FIGS. 48A to 48C are timing charts showing function of the focusdetecting device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 7 is a block diagram showing the entire structure of a single-lensreflex camera equipped with a focus detecting device of the presentinvention.

Referring to FIG. 7, an interchangeable lens 10 is detachably mountableon a camera body 20. In the mounted state of the lens 10, a phototakinglight beam coming from an object is transmitted by a phototaking lens11, then partly reflected by a main mirror 21 provided in the camerabody 20 toward a finder, and is further transmitted by a focusing screen23, a pentagonal prism 24 and an eyepiece lens 25 whereby an imageformed on the focusing screen is observed by the photographer. Theremaining part of the light beam is transmitted by the main mirror 21,then reflected by a sub mirror 22 and guided as a focus detecting lightbeam to a focus detecting optical system 30.

Said focus detecting optical system 30 can be constructed, for example,as shown in FIG. 1, wherein an object image focused by the phototakinglens 11 is re-focused on photosensor elements of a photoelectricconverting device 32. The light-receiving face of the photosensorelements constitutes a focus detecting plane (conjugate with the film)of the focus detecting optical system 30. Thus the photosensor elementsof the photoelectric converting circuit 32 effect photoelectricconversion on the object image re-focused by the focus detecting opticalsystem 30 thereby generating object image signals.

Said image signals are supplied to a microcomputer 400 of the camerabody, for use in various calculations to be explained later.Functionally, the microcomputer 400 is equipped with a portion 400A forcalculating the peripheral light amount of the focus detecting opticalsystem; a memory portion 400B for information on the focus detectingoptical system; a light amount distribution detecting portion 400C; anda focus detecting calculating portion 400D, of which details will beexplained later. there are also provided known internal mechanisms ofcamera, such as a shutter device 27 and an unrepresented film advancingmechanism.

An auto focusing (AF) motor 51 is driven according to the defocus amountcalculated by the microcomputer 400, and axially moves a focusing lensof the phototaking lens 11, through a body transmission system 52, aclutch 53, couplings 54, 18 and a lens transmission system 13. Anencoder 55 detects the number of rotations of the AF motor 51 and entersit into the microcomputer 400.

A lens CPU 12 generates information on the peripheral light amount ofthe phototaking lens 11, the F-number f0 of the exit pupil at thefully-open diagrams aperture, and the position of the exit pupil (d1 inFIG. 2) with respect to the film plane, and enters said information intothe microcomputer 400 through couplings 59E, 19E. When said informationvaries by the focusing or zooming of the phototaking lens 11, the lensCPU 12 detects the focusing and zooming positions and varies saidinformation according to the detected focusing and zooming positions.

The information on the peripheral light amount of the phototaking lens11 is given as shown in FIG. 8, by a function F(d) of the distance dfrom the optical axis on the image plane. The information on theperipheral light amount can be generated by defining coefficients a₀ , .. . , a_(n) of the following polynomial approximation of d:

    F (d) =a0×d.sup.0 +a1×d.sup.2 +a2×d.sup.2 +. . . +an×d.sup.n                                         (1).

If the phototaking lens 11 has the exit pupil of a special shape, thelens CPU 12 generates information on the shape and position of thediaphragm instead of the F-number. For example, in case of a reflexlens, the lens CPU generates information on the circumscribed F-numberand inscribed F-number of the diaphragm and the pupil positions thereof.

The memory portion 400B for the information of focus detecting opticalsystem stores in advance information on the peripheral light amount ofthe focus detecting optical system 30, pupil position (d0 in FIG. 2) forfocus detection, and shape and position of pupil diaphragm for focusdetection. For example, in case of focus detecting pupil diaphragm 305Ashown in FIG. 3, the information on the shape and position of the focusdetecting pupil diaphragm are external radius r0, internal radius r1 andcenter d2 of the internal radius r1.

The peripheral light amount calculating portion 400A for the focusdetecting optical system 30 converts the peripheral light amount on aplane of the photosensor elements of the photoelectric convertingcircuit 32 into the position of the photographed image plane, in a formsimilar to the information on the peripheral light amount of thephototaking lens 11. However, since the focus detecting optical system30 is eccentric, the information on peripheral light amount is not pointsymmetric with respect to the center, as in the equation (1). In suchcase, the peripheral light amount can be represented by the followingequation (2), utilizing two-dimensional axes X, Y with centers at pointscorresponding to the optical axis (for example B', B" in FIG. 2):

    Ga(x, y)=Ha(x)·Ia(y)

    Ha(x)=b.sub.0 ×x.sup.0 +b.sub.1 ×x.sup.1 +. . . +b.sub.n ×x.sup.n

    Iz(y)=c.sub.0 ×y.sup.0 +c.sub.1 ×y.sup.1 +. . . +c.sub.n ×y.sup.n                                            (2)

When there are provided two pairs of focus detecting optical systems 30as shown in FIG. 1, the peripheral light amount information Ga(x, y),Gb(x, y), Gc(x, y) and Gd(x, y) are required for the respectiveseparator lenses 303A, 303B, 303C and 303D, but, if the lenses 303A and303B, and 303C and 303D, are symmetrical with respect to the opticalaxis, the amount of information can be compressed since Gb(x, y)=Ga(-x,y) and Gd(x, y)=Gc(x, -y). Also the peripheral light amount informationmay be represented by the light amount in each of small cells (x, y)into which the photoelectric converting plane is divided. Also theperipheral light amount information of the focus detecting opticalsystem may be determined by the output of the photosensor elements in astate in which an object of uniform luminocity is focused on the focusdetecting plane (conjuagate with the film) of the focus detectingoptical system, or by the design data of the optical system.

The light amount distribution detecting portion 400C detects thedistribution of light amount on the photosensor elements, for an objectof uniform luminocity, based on the information from the lens CPU 12 andthe peripheral light amount calculating portion 400A. Said distributionis determined for each image formed by the focus detecting opticalsystem 30. For example, in case of the optical system shown in FIG. 1,the light amount distribution is determined for each of the four lenses303A, 303B, 303C and 303D.

Calculation of the light amount distribution will be explained in thefollowing.

The light amount distribution for example of the re-focusing lens 303Bis determined in the following manner, in case the phototaking lens 11has the exit pupil at d1, a fully-open F-number f0 and a peripherallight amount information F(x, y); and the focus detecting optical system30 has a structure shown in FIG. 1 with the focus detecting pupil at d0,the focus detecting pupil diaphragm of circular shape with a radius r2and the center at (xb, 0) on the focus detecting pupil plane as shown inFIG. 9 and with the peripheral light amount information Gb (x, y).

A light beam passing through a point (x0, y0) of the aperture 300A andthe re-focusing lens 303B forms, on the exit pupil plane of thephototaking lens 11, a circle P with a radius r3 and with the center at(x1, y1) as shown in FIG. 10. On the other hand, the exit pupil of thephototaking lens 11 on the pupil plane forms a circle Q with a radius r4and with the center at (0, 0). Consequently the vignetting informationJb(x0, y0) of the light beam passing through the coordinate (x0, y0) andthe lens 303B is given by dividing the common area A1 of the circles Pand Q with the area A2 of the circle P:

    Jb(x, y)=A1/A2

    x1=x0+(xb-x0)-d1/d0

    y1=y0-y0-d1/d0

    r3=r2-d1/d0

    r4=d1/(2f0)                                                (3)

Thus the vignetting information Jb(x, y) can be determined for anyarbitrary coordinate (x, y). Consequently the final light amountdistribution information Kb(x, y) can be represented as (4):

    Kb(x, y)=F(x, y)-Gb(x, y)-Jb(x, y)                         (4)

Similarly the vignetting information Ja(x, y), Jc(x, y) and Jd(x, y) forthe lenses 303A, 303C and 303D can be determined in a similar manner,and the light amount distribution information Ka(x, y), Kc(x, y) andKd(x, y) can be obtained based on other peripheral light amountinformation Ga(x, y), Gc(x, y) and Gd(x, y) of the focus detectingoptical system 30. FIGS. 11A and 11B illustrate the behavior of thelight amount distribution information Ka(x, y).

The focus detection calculating portion 400D detects the defocus amountbetween the current image plane of the phototaking lens 11 and the filmplane, by applying a known focus detecting calculation on the objectimage signals released by the photoelectric converting circuit 32.

The defocus amount can be determined in the following manner, forexample for a focus detecting optical system 30 shown in FIG. 1 and fordata ap, bp (p=1-n) and cq, dq (m=1-m) obtained by A/D conversion fromthe image signals of the photosensor elements 304A, 304B, 304C, 304D ofthe photoelectric converting device 304.

For the purpose of simplicity, the following explanation on thecorrelation calculation is only given on the output data ap, bp, but asame process is applied also to the data cq, dq. At first a correlationamount C (L) is determined from the output data ap, bp by a correlationcalculation shown by the following equation (5): ##EQU1## wherein L isan integer, indicating the amount of relative shift of paired outputdata of the photosensor elements, represented by the pitch ofarrangement of photosensor cells. Also in the summation of the equation(5), the range of the parameter i is suitably determined according tothe shift amount L and the data number n.

The calculation of the equation (5) provides a minimum correlation C(L)at a shift amount L=kJ where the correlation is highest. Then a minimumvalue C(L)min=C(km) for continuous correlation is determined by athree-point interpolation method shown in (6):

    km=kj+D/SLOP

    C(km)=C(kj)-|D|

    D={C(kj-1)-C(kj+1)}/2

    SLOP=MAX(C(kj+1)-C(kj), C(kj-1)-C(kj))                     (6)

The defocus amount DEF can be determined in the following manner fromthe shift amount kj determined by the equations (6):

    DEF=KX×PY×km                                   (7)

wherein PY is the pitch of arrangement of the photosensor cellsconstituting the photosensor elements of the photoelectric convertingdevice 304, and KX is a coefficient determined by the structure of thefocus detecting optical system shown in FIG. 1.

Also the parameters C(km) and SLOP obtained from the equations (6) allowto judge the reliability of the defocus amount DEF, and said parametersare used for determining whether the focus detection is possible or not.

The foregoing explanation has been limited to the calculation ofcorrelation between a pair of one-dimentional data, but said calculationcan be easily expanded to a case where two-dimensional data are obtainedfrom two-dimensional photosensor elements of the photoelectricconverting circuit.

The focus detection calculating portion 400D also determines the rangedata, to be employed in the correlation calculation according to theequations (5), based on the light amount distribution information. Forexample, when the light amount distribution information Ka(x, y) isdetermined as shown in FIG. 12 and the data al-an of the photosensorelement 304A are set on the image field, data au-aw with light amountsat least equal to a predetermined value t % are employed in thecorrelation calculation. The range of data to be employed in thecorrelation calculation can be similarly determined for other data bi,ci and di. In this manner it is rendered possible to reduce theunbalance between the data resulting from loss in the light amount, inthe correlation calculation, and to improve the accuracy of focusdetection.

Furthermore, the calculating portion 400D may effect conversion of thedata to be employed in the correlation calculation according to theequations (5), based on the light amount distribution information. Forexample, if said information indicates significant loss in light amount,data may be converted by a filtering calculation for low frequencycomponents removal according to the equation (8):

    a'i=-ai+2-a(i+1)-a(i+2)                                    (8)

The data a'i, b'i, c'i and d'i converted according to the equation (8)are used, instead of the original data ai, bi, ci and di, in thecorrelation calculation according to the equations (5). Such conversionallows to eliminate the low frequency components of the image signals,resulting from the loss in light amount, thereby improving the accuracyof the focus detection.

Furthermore, the calculating portion 400D may vary, according to thelight amount distribution information, the threshold reference value injudging the reliability of the defocus amount DEF by the parametersC(km) and SLOP obtained from the equations (6). For example, if saiddistribution information indicates a significant loss in light amount,said reference value may be lowered to avoid the reduction in thereliability resulting from the loss in light amount. In this manner aconstant determination whether the focus detection is possible or notcan be obtained for a same object, regardless of the presence or absenceof loss in light amount.

Furthermore, the object image signals may be corrected, according to thelight amount distribution information, to image signals corresponding toa uniform state without loss in light amount. For example, if thephotoelectric converting device is composed of a pair of two-dimensionalsensors with output image signals Sa(x, y) and Sb(x, y), with lightamount distribution information Ka(x, y) and Kb(x, y), said correctioncan be made according to the following equation (9):

    S'a(x, y)=Sa(x, y)/Ka(x, y)

    S'b(x, y)=Sb(x, y)/Kb(x, y)                                (9)

Such correction corrects the loss in light amount included in the imagesignals, thereby enabling the calculating portion 400D to effect exactcorrelation calculation and improving the accuracy of focus detection.

The above-explained calculations are conducted according to a program ofthe microcomputer 400.

FIG. 13A shows a main flow chart of said program. At first a step S100calculates the light amount distribution information ka-kd. Then a stepS200 effects a predetermined process on the image signals, based on thuscalculated distribution information ka-kd, and a step S300 determinesthe defocus amount by a focus detecting calculation based on thusprocessed image signals. The lens is driven based on said defocusamount, according to an unrepresented control sequence.

The light amount distribution information ka-kd are determined accordingto a flow chart shown in FIG. 13B.

A step S101 determines the peripheral light amount F(d) of thephototaking lens 11 according to the equation (1), by fetching saidequation (1), stored in the lens CPU 12, into the microcomputer 400 ofthe camera body. A next step S102 determines the peripheral lightamounts Ga(x, y)-Gd(x, y) of the focus detecting optical system from theequations (2). Then a step S103 determines the vignetting informationJa(x, y)-Jd(x, y) from the equations (3), and a step S104 determines thelight amount distribution in formation ka (x, y)-kd (x, y) from theequation (4).

FIG. 13C shows a pre-editing procedure for the image signals.

A step S201 discriminates whether the light amount distributioninformation ka(x, y)-kd(x, y) are smaller than a reference value. Iflarger, said step S201 is negated and a step S202 stores the imagesignals as Sa(x, y)-Sd(x, y) in a memory. If smaller, the sequence jumpsto a step S203 for discriminating whether the comparison has beencompleted for all the pixels, and, if completed, the sequence of FIG.13C is terminated. Thus the image signals are stored in the memory onlywhen the distribution information ka(x, y)-kd(x, y) are larger than thereference value.

FIG. 13D is a flow chart of focus detecting calculation.

A step S301 determines the correlation C(L) from the pre-edited imagesignals, according to the known calculation of the equations (5). Then astep S302 determines the shift amount kj of high correlation accordingto the equations (6), and a step S303 determines the defocus amount fromthe equations (7).

The pre-editing procedure shown in FIG. 13C stores only the imagesignals of which light amount distribution information are larger thanthe reference in the memory, but it is also possible to store all theimage signals in the memory by applying the correction of the equations(9) based on the light amount distribution information ka-kd.

Also in a pre-editing procedure shown in FIG. 13F, a step S221discriminates the presence of light amount distribution informationka-kd smaller than the reference value, and, if affirmative, a step S222effects filtering for removing the low frequency components according tothe equations (8), and thus filtered image signals are used for focusdetecting calculation.

The focus detecting optical system may be constructed as shown in FIG.1, or as shown in FIG. 14. The structure shown in FIG. 14 is composed ofa field mask 300 having a two-dimensional aperture 300A; a field lens301; a diaphragm mask 302 having a pair of apertures 302A, 302B; a pairof re-focusing lenses 303A, 303B; and a photoelectric converting device304 provided with photosensor areas 304A, 304B in which photosensorelements are two-dimensionally arranged. Such structure realizestwo-dimensional arrangement of focus detecting areas (AF areas) on theimage plane, and enables arbitrary change of the focus detecting areasbased on the selection of AF areas or on the result of viewing pointdetection to be explained later.

Also the focus detecting optical system 30 may be constructed as shownin FIG. 15. In said system, the diaphragm mask 302 is composed of aphysical device capable of electrically varying the light transmittance,such as an electrochromic (EC) or liquid crystal (LC) device, and theapertures thereof can be shifted between those 302A, 302B shown in FIG.14 and those 302A', 302B'with smaller radius of circumscribed circles asshown in FIG. 15, by electrical control from the outside. Thus, in caseof vignetting with the apertures 302A, 302B, said apertures can beswitched to the apertures 302A', 302B' with smaller radius ofcircumscribed circles thereby reducing the focus detecting diaphragms onthe focus detecting pupil plane and thus avoiding the vignetting. In thestructure shown in FIG. 15, the circumscribed circles are reduced by asize reduction of the apertures 302A', 302B', but, for a lens with anannular exit pupil such as a reflex lens, the inscribed circles of theapertures 302A', 302B; can be increased in order to avoid vignetting ofthe focus detecting diaphragm inside the annular exit pupil.

Furthermore, the focus detecting optical system 30 may be constructed asshown in FIG. 16. In this case the diaphragm mask 302 and there-focusing lenses are different in structure from those in FIG. 15, andthe apertures 302A, 302B of the diaphragm mask 302 shown in FIG. 15 canbe shifted to those 302C, 302D with a different direction of arrangementby external electrical control. Re-focusing lenses 303C, 303D areprovided behind said apertures 302C, 302D. Such structure allows toselect the apertures arranged in a direction of easier focus detection,depending on the pattern of the object, thereby improving the accuracyof focus detection. As the photoelectric converting device 304 has atwo-dimentional photosensor area 304E, a common photoelectric convertingarea may be used for the apertures 302A, 302B and re-focusing lenses303A, 303B, or the apertures 302C, 302D and re-focusing lenses 303C,303D. The problem of image overlapping can be avoided because the imagesby the lenses 303A, 303B and those by the lenses 303C, 303D are notformed at the same time.

In the structure shown in FIG. 16, the direction of arrangement of theapertures 302C, 302D is perpendicular to that of the apertures 302A,302B, but there may be naturally selected other directions ofarrangement.

In the structures shown in FIGS. 15 and 16, a physical device isemployed for switching the form of the apertures, but plural aperturesmay be switched in mechanical manner.

In the following there will be explained an embodiment of the presentinvention applied to a single-lens reflex camera, with reference to FIG.17 and ensuing drawings.

Function of AF detection system controlling CPU

The AF detection system controlling CPU 33 has the functions ofselecting the aforementioned AF diaphragm according to an instruction bythe AF calculating CPU 40 to be explained later or according to its owndiscretion, controlling the functions such as charge accumulation andcharge transfer of the photoelectric converting device 32 with alreadyknown control signal s and transfer clock signals, and storing thetransferred image signals into the memory 34 after A/D conversion.

The operations of said controlling CPU 33 will now be explained indetail, with reference to FIGS. 17 to 25.

FIG. 17 is a flow chart showing an example of control sequence of the AFdetection system controlling CPU 33. A step S000 effects chargeaccumulation in the photoelectric converting device 32 for apredetermined accumulating time. Upon completion of the accumulation, astep S005 changes a header indicating the memory storage area of theA/D-converted output data of the photoelectric converting device 32.Then a step S010 effects transfer of the output of said device 32, A/Dconversion, data correction and storage in the memory, for each data.Said data correction includes the calculation according to the equations(9) for correction for the peripheral light amount. For said correctionthe controlling CPU 33 incorporates the information of the focusdetecting optical system, and receives the information on thephototaking optical system from the lens CPU 12. Upon completion oftransfer of all the output data, a step S015 changes the header,indicating the latest data storage area, to the current data storagearea, and a step S020 determines the next accumulating time in such amanner that the peak value of the obtained image data becomes equal to apredetermined value. Then the sequence returns to the step S000 torepeat the above-explained sequence.

FIG. 18 conceptually shows the changes in the data storage areas in thememory 34 in the above-explained procedure. If a latest data storagearea and a data storage area currently under data storage are arrangedas indicated "this time", the current data storage area will become thelatest data storage area in the next time. Since the headers of thelatest data storage area and the current data storage area are stored inthe memory 34, the AF calculating CPU 40 can always utilize the latestdata from the latest data storage area for the focus detectingcalculation by reading the header of said area from the memory 34. Alsosince the control operation for the photoelectric converting device 32and the focus detecting calculation are separated, these two operationscan be conducted in parallel manner, so that the efficiency in time orthe response of focus detection can be improved.

FIG. 19A is a timing chart of the above-explained procedure, in whichthe signal transfer is started immediately after the completion of thecharge accumulation of the photoelectric converting device 32, and thenext charge accumulation is started immediately after the completion ofthe signal transfer. In case of FIG. 19A the charge accumulation and thesignal transfer are mutually separated in time, but these operations maymutually overlap as shown in FIGS. 19B or 19C. If the chargeaccumulating time is longer than the signal transfer time, the signaltransfer and the next charge accumulation are started immediately afterthe completion of the charge accumulation, as shown in FIG. 19B. On theother hand, if the charge accumulating time is shorter, as shown in FIG.19C, the signal transfer is started immediately after the completion ofthe charge transfer, and the next charge accumulation is started at asuitable timing in such a manner that said next charge accumulation willbe completed immediately after the completion of the signal transfer.Such mutually overlapping charge accumulation and signal transfer intime improves the efficiency in time, or the response of the focusdetecting operation, and allows to absorb the loss in response,resulting from the increase in number of data in the use of atwo-dimensional photoelectric converting device.

As alternative method for absorbing such loss in response, a rectangulartwo-demensional photosensor area as shown in FIG. 20A may be dividedinto n blocks YBl-YBn oblong parallel to the X-axis, and chargeaccumulation and signal transfer may be conducted in time-separatedmanner for each block. A structure shown in FIG. 20A ensures thesimultaneous character of data in the X-direction, and is thereforebetter matched with the apertures 302A, 302B arranged in theX-direction, on the diaphragm mask shown in FIG. 21. On the other hand,in case of using the apertures 302C, 302D arranged in the Y-direction,it is preferable to divide the photosensor area into n blocks XBl-XBnoblong in a direction perpendicular to the X-axis, as shown in FIG. 20B,and to effect the charge accumulation and the signal transfer intime-separated manner for each block, thereby ensuring simultaneouscharacter of the data in the Y-direction.

Also in case the light source is of a high luminocity and involvesflickering, whereby the output of the charge accumulation varies evenfor a same accumulating time, depending on the timing of chargeaccumulating operation in the flickering cycle, the charge accumulatingoperation may be divided into plural portions as shown in FIG. 19D,thereby effecting the accumulation plural times in a flickering cycle ofthe light source, thereby alleviating the influence of said flickering.

Also in case the peripheral light amount is lowered as shown in FIGS.11A and 11B or in FIGS. 5B to 5D, the charge transfer time may be savedby effecting the normal transfer operation only in an image area to beused in the focus detecting calculation and a high-speed transferoperation in other areas. For example, if the data usable for focusdetection are defined by broken-lined areas in FIG. 22A or 22Brespectively corresponding to the use of apertures 302A, 302B arrangedin the X-direction on the diaphragm mask shown in FIG. 21 or those 302C,302D arranged in the Y-direction, the normal transfer operation isconducted only for the output data corresponding to the interior of thebroken lines and high-speed transfer operation is conducted, without theA/D conversion and the storage in the memory, for other areas. Alsoinformation indicating the correlation between the data stored in thememory by normal transfer operation and the areas thereof on thephotosensor areas is stored in the memory and is utilized in the focusdetecting calculation by the AF calculating CPU 40.

In case a two-dimensional image sensor is used as the photoelectricconverting device 32, the amount of signal is enormous, so that aconsiderable time is consumed in the signal transfer and the A/Dconversion. Therefore, if the charge accumulating time is extended dueto a low light intensity, the charge accumulation and the signaltransfer of the image sensor cannot be accommodated within apredetermined time and the response is deteriorated. In order to avoidsuch situation, it is possible, at a low light intensity, to use only apart of the entire output of the image sensor for the focus detection,to effect the transfer and A/D conversion at the normal rate only suchused part of the sensor output while to transfer the output of otherunused parts at a higher rate without A/D conversion, or to extract theimage sensor output only in the used part, thereby accommodating the sumof the charge accumulating time and the signal transfer time in apredetermined period. In such low light intensity situation, the dataused for focus detection are desirably obtained from the central portionof the image field.

In the foregoing description, the charge accumulating time of thephotoelectric converting device 32 is so determined that the image datahave a predetermined peak value, but such determination of the nextaccumulating time by the image data may result in an oscillationphenomenon in case the object is illuminated by a light source withcyclically varying intensity, such as a fluorescent lamp. Though theremay be provided a monitor device in the vicinity of the photoelectricconverting device for monitoring the average intensity of object imageon real time basis and terminating the charge accumulation of thephotosensor area when the monitor signal reaches a predetermined value,the peak value may exceed the range of A/D conversion for certainobjects composed for example of white lines on a black background.

FIGS. 23 and 24 show a method for controlling the charge accumulatingtime for resolving such drawback.

Referring to FIG. 23, the monitor signal is reset to a value VRsimultaneously with the start of charge accumulation. The monitor signalincrease according to the average brightness of the object image, andreaches a predetermined value Vs after a time Tm from resetting. The AFdetection system controlling CPU 33 determines the current accumulatingtime Ti according to the following equation, based on the peak valuePEAK of the previous image data shown in FIG. 24, the average value AVthereof, the previous accumulating time Til, the target peak value, thecurrent monitor time Tm, and a predetermined value K1, and terminatesthe accumulation at the time Ti from the start thereof:

    Ti=(K1×Pt×Tm)/AV

    or

    Ti=(Pt×Tm×Til)/(PEAK×Tml)                (10).

Also in case a lowered peripheral light amount is identified from theinformation on the focus detecting optical system and the information onthe phototaking optical system received from the lens CPU 12, or in caseof a request from the AF calculating CPU 40 (for example for expandingthe range of detectable defocus amount in case of disabled focusdetection), the AF detection system controlling CPU 33 may switch theapertures 302A, 302B of the diaphragm mask shown in FIG. 25 to those302C, 302D with less tendency of vignetting. Also in response to arequest from the AF calculating CPU 40 (for example in case of disabledfocus detection due to absence of vertical patterns), or in response toa vertical/horizontal selection by an AF area selecting device 66 to beexplained later (for selecting either the horizontal photosensorelements 304A, 304B or the vertical photosensor elements 304C, 304D forfocus detection), or in response to the detection by a body positiondetecting device 69, the apertures 302A, 302B of the diaphragm maskshown in FIG. 21 may be switched to those 302C, 302D. Information onsuch switching is supplied to the AF calculating CPU 40, which effectsprocessing accordingly.

Function of AF Calculating CPU

Referring to FIG. 26, the AF calculating CPU 40 has a function ofeffecting known focus detecting calculation on the image data stored inthe memory 34, thereby determining the defocus amount of the phototakingoptical system. For example, in case of employing a focus detectingoptical system as shown in FIG. 1, said CPU effects, as disclosed in theU.S. patent application Ser. No. 457,408 of the present applicant, thefocus detecting calculation on each of plural blocks formed in the focusdetecting area, and selects an optimum defocus amount from thuscalculated plural defocus amounts, according to various principles. Thefocus detecting calculation conducted by the AF calculating CPU 40 isprincipally composed, as shown in FIG. 27, of a step S030 for datacorrection and conversion, a step S035 for selecting the focus detectingarea, a step S040 for block division, a step S045 for defocus amountcalculation for each block, and a step S050 for final defocus amountselection, and said CPU 40 repeats these steps. These steps will beexplained in detail in the following.

The data correction/conversion step also includes the calculationaccording to the equations (9) for peripheral light amount correction.The AF calculating CPU 40 executes the correction of the equations (9)by determining the light amount distribution information, based on theinformation of the focus detecting optical system incorporated in saidCPU or received from the AF detection system controlling CPU 33 and theinformation of the phototaking optical system received from the lens CPU12.

If the loss in light amount is identified significant from the obtainedlight amount distribution information, data conversion is conducted byfiltering for eliminating the low frequency components as shown by theequations (8). Such data conversion may be applied solely to an objectcontaining a large amount of high frequency components, as identified bythe contrast of the object. For example, an image signal as shown inFIG. 28A or 28B is divided into plural blocks, and contrast CON isdetected in each of said blocks according to the equation (11). Apredetermined contrast is not obtained in any of the blocks, the objectis identified as a low-frequency object and the data conversion of theequations (8) is not applied. If said predetermined contrast is obtainedin at least a block, said data conversion is conducted:

    CON=Σ|ai-a(i+1)|                   (11).

Such selective application of the data conversion by filtering,according to the image contrast, enables focus detecting calculation onan object containing a large amount of low frequency components withoutfiltration of such low frequency components, thereby improving theaccuracy of focus detection.

The focus detection area selecting step selects, for example, either anarrow spot area at the center of image field or a wide area for focusdetection, as shown in FIG. 29A, by a suitable method. Also there may bearbitrarily selected a focus detecting area or areas at arbitraryposition(s), as shown in FIG. 29B, either manually by the AF areaselecting device 66 or by the viewing point detecting device 68.

FIGS. 30A and 30B illustrate an example of the viewing point detectingdevice 68. A planar infrared-emitting element 683 projects infraredlight through a half mirror 681, a lens 680 and an infrared-reflectingdichroic mirror 682 provided in the eyepiece lens 25, to an eye 685 ofthe finder viewing person. In this optical system, the shapes andpositions of the optical components are so selected that thelight-emitting face of said element 683 overlaps in shape and positionwith the image field in the view-finder. The infrared light projected tothe eye 685 of the observer is reflected by a retina 686, reflected bythe dichroic mirror 682 in the eyepiece lens 25, transmitted by the lens680 and the half mirror 681 and is received by a planar photosensor 684.As the reflecting efficiency is higher in the viewing direction than inother directions, an area of the photosensor 684 receives a largeramount of light, corresponding to an area of the finder screen watchedby the observer. In order to avoid the influence of infrared lighteventually coming from the view-finder, there is detected the differencein the light amount distribution received by the planar photosensor 684between the light-emitting state of the planar infrared-emitting device683 and the deactivated state thereof, as shown in FIG. 30B, and theviewing point is detected from an area of maximum light reception insaid distribution.

The result of said viewing point detection may be used for selecting thefocus detecting area as explained before, or for selecting an area forspot light metering. In the above-explained structure, the planarphotosensor 684 may be composed of a two-dimensional CCD sensor, or aposition sensor for detecting the center of gravity of light reception.Also the planar infrared-emitting device 683 may be replaced by atwo-dimensional beam scanning. Also since said detection of viewingpoint may be erroneously affected by the winking of the observer, thetotal received light is monitored and data with lowered total receivedlight are excluded from said detection. Also the stability of detectionis improved by reducing the response in time, for example by statisticaltreatment, in order not to follow the winking or momentary fluctuationof the viewing point.

The step S040 for block division in FIG. 27 divides the focus detectingarea, selected in the preceding step, into plural blocks according tothe object pattern. For example, an image signal as shown in FIG. 28A or28B is divided into plural blocks, and a contrast detection according tothe equation (11) is conducted in each block. If a predeterminedcontrast is not obtained in any of the blocks, the object is identifiedas a low-frequency object, and the focus detecting area is divided intoa fewer number of blocks as shown in FIG. 28C (broken lines indicatingthe boundaries of blocks). If said predetermined contrast is obtained inat least one block, the area is divided into a larger number of blocksas shown in FIG. 28D.

The step S045 for defocus amount calculation for each block applies theknown focus detecting calculation to each of the blocks divided in thepreceding step. Thus the defocus amount can be determined in each of theblocks.

The step S050 for defocus amount correction applies a correction, basedon the optical aberrations of the phototaking optical system, to thedefocus amount, according to the position of the block. For example, ifthe information on image plane curvature is sent from the lens CPU 12 inthe form of coefficients M₂ , M₄, . . . defining a function S (d) of thedistance d from the center of image field, as indicated by:

    S(d)=M.sub.2 ×d.sup.2 +M.sub.4 ×d.sup.4 +. . . (12)

the correction on the defocus amount of a block can be determined bysubstituting the distance dc from the center of image field to thecenter of said block into the equation (12).

Corrections for other aberrations can be made in a similar manner.

The step S055 for selecting final defocus amount determines a defocusamount from the above-mentioned plural defocus amounts, according to apredetermined algorithm. For example, if the selecting algorithm isbased on priority in the center, there is selected the defocus amount ofa block which is closest to the center of image field and in which thefocus detection is possible. Also there is selected a defocus amountindicating a shortest object distance in case of priority to theshortest distance; a defocus amount indicating a longest object distancein case of priority to the longest distance; an average of thecalculated defocus amounts or an average weighted by reliability in caseof priority to the average; or a defocus amount with the smallestabsolute value in case of priority to the current status.

Thus a defocus amount is finally determined through the above-explainedsteps. In the following there will be given a detailed explanation onthe variations of area selection and algorithm selection in the finaldefocus amount selecting step.

In the manual area selection, the AF area can be selected as shown inTab. 1, by an AF area selecting device 66 provided on the camera body.

Referring to Tab. 1, a view point detection mode selects an area basedon the result obtained by said viewing point detecting device 68; acenter spot mode selects a spot area at the center of image field asshown in FIG. 29A; a selected spot mode selects spot areas arbitrarilyselected in the image field as shown in FIG. 29B; a wide mode selects awide area shown in FIG. 29A; and horizontal and vertical modes selectareas respectively corresponding to horizontal photosensor elements304A, 304B or vertical photosensor elements 304C, 304D in the focusdetecting optical system shown in FIG. 1. Also a center spot-wide modeselects the center spot area before focusing and then the wide AF areaafter in-focus state is once obtained. Such manual selection of the AFarea enables the photographer to select an optimum area for the object.

Also the algorithm may be switched as indicated in the right-hand columnof Tab. 1 in connection with the selection of the AF area. As plural AFareas may be selected in the view point detection mode or in theselected spot mode, the algorithm is shifted to an average priority modeto approximately focus to all the plural objects. In the center spotmode of the AF area selection, as the AF area is selected at the centerof image, the algorithm is shifted to a center priority mode to focus tothe object at the center or image field. Also as a wide AF area isselected in the center spot-wide mode, the wide mode or the horizontalmode, the algorithm is set at a minimum distance priority→presentcondition priority mode, thereby focusing to a closest object until anin-focus state is obtained and then increasing the stability by thepresent priority mode avoiding the unnecessary lens drive by an eventualobstacle at the even shorter distance. In the vertical mode where the AFarea is relatively narrow with limited chance of appearance of anunwanted object, the algorithm is set at the minimum distance prioritymode to constantly focus to an object at the shortest distance.

In case of manual algorithm selection, the algorithm can be selected asshown in Tab. 2, by an AF object selecting device 67 provided on thecamera body.

Referring to Tab. 2, a center priority-present condition priority modeindicates to adopt the center priority mode before focusing and thepresent condition priority mode after the in-focus state is reached, anda minimum distance priority-present condition priority mode indicates toadopt the minimum distance priority mode before focusing and the presentcondition priority mode after the in-focus state is reached. Such manualalgorithm selection enables the photographer to select an optimumalgorithm for the object.

Also the AF area may be switched as indicated in the center column ofTab. 2, in connection with the algorithm selection. As the centerpriority mode or the minimum distance priority mode of algorithm matchesbetter with a smaller AF area, the center spot mode is selected for theAF area. In the average priority mode, the maximum distance prioritymode or the minimum distance priority-present condition priority mode ofthe algorithm selection, there is preferred a larger AF area so that thewide mode is selected for the AF area. In the center priority→presentcondition priority mode of algorithm selection, the AF area is selectedat the center spot-wide mode in order to maintain a small AF area beforefocusing and to improve the stability with a wide AF area after thein-focus state is reached.

In the following there will be explained an embodiment in which the AFarea and the algorithm are not selected by exclusive selecting devicestherefor but are selected in connection with the function of a selectingdevice for other operations of the camera.

In connection with the selection of the light metering mode by aselecting device 71 as shown in the left-hand column in Tab. 3, among acenter spot mode (light metering in a relatively narrow area at thecenter of image field), a selected spot mode (light metering inrelatively narrow areas at arbitrary positions in image field), apartial mode (light metering in a wider area at the center of image), acenter weighted mode (light metering over the entire image field withweight in the center), or a multi mode (light metering with the entireimage field divided into plural areas), the AF area and the algorithmare selected as respectively indicated in the center and right→handcolumns in Tab. 3. In the center spot light metering mode in whichemphasis is given to the central part of the image field, the centerspot AF area is selected and the center priority mode is selected forthe algorithm. In the selected spot light metering mode, selectingplural positions in the image field, the selected spot mode is selectedalso for the AF area, and the minimum distance priority mode is selectedfor the algorithm. In case of the partial or center weighted lightmetering mode, selecting a relatively wide area, the AF area selectionis set at the center spot-wide mode and the algorithm is set at thecenter priority-present condition priority mode. In case of the multilight metering mode where the entire image field is used for metering,the wide mode is selected for the AF area and the minimum distancepriority-present condition priority mode is selected for the algorithm.In this manner satisfactory correlation is maintained between the AFarea and the light mete ring area, and there can be improved thestability of auto focusing and the selectively for the object.

Also in connection with the selection of the auto exposure (AE) mode bya selecting device 70 as shown in the left-hand column in Tab. 4, amongan aperture priority mode, a shutter speed priority mode or a programmedmode, the AF area and the algorithm may be selected as respectivelyshown in the center and right-hand columns. In case of the aperturepriority AE mode, which is mostly used for photographing an objectstopped at the center of image field, the center spot→wide mode isselected for the AF area and the center priority→present conditionpriority mode is selected for the algorithm, in order to improve theselectivity for the object. In case of the shutter speed priority AEmode, mostly used for a moving object, the wide mode is selected for theAF area and the minimum distance priority mode is selected for thealgorithm, in order to improve the object following ability. In case ofthe programmed mode, often used by beginners or in snap photography, thewide AF area mode is selected and the minimum distance priority-presentcondition priority mode is selected for the algorithm, in order toimprove the object following ability and the stability. In this mannerthe AF area and the algorithm optimum for the object can be selected bymerely selecting the AE mode according to the object.

Also in connection with the selection of the film winding mode by aselecting device 65 as shown in the left-hand column of Tab. 5, among asingle frame mode, a continuous high-speed mode, a continuous low-speedmode and a self-timer mode, the AF area and the algorithm may berespectively selected as shown in the center and right-hand columns. Incase of the single frame winding mode, often used for photographing anobject stopped at the center of image field, the AF area and thealgorithm are respectively set at the center spot mode and the centerpriority mode, in order to improve the selectivity for the object. Inthe continuous high-speed winding mode, often used for a moving object,the AF area and the algorithm are respectively set at the wide mode andthe minimum distance priority-present condition priority mode, in orderto improve the object following ability and the auto focusing stability.In case of the continuous low-speed winding mode, which is between thesingle frame mode and the continuous high-speed mode, the AF area is setat the center spot-wide mode while the algorithm is set at the minimumdistance priority-present condition priority mode, thereby mixing thefollowing ability and the selectivity for the object. In case of theself-timer winding mode, in which the position of the main object cannotbe predicted in the image field, there are selected the wide AF areamode and the minimum distance priority algorithm, in order to securelyfollow the object. In this manner, mere selection of the film windingmode according to the photographing situation enables to select theoptimum AF area and algorithm for said situation.

Also in connection with the selection of the photographing mode by aselecting device 64 as indicated in the left-hand column of Tab. 6,among a sports mode, a portrait mode, a snap mode, a landscape mode anda close-up mode, the AF area and the algorithm may be selectedrespectively as shown in the center and right-hand columns. Selection ofa photographing mode automatically selects a light metering mode, an AEmode, a film winding mode and a focusing mode optimum for eachphotographing condition. In the sports photographing mode, mostly usedfor a moving object, there are selected the wide AF area and the minimumdistance priority→present condition priority mode for the algorithm, forimproving the object following ability. In case of the portraitphotographing mode, mostly used for a stopped object, there are selectedthe center spot mode for the AF area and the minimum distance prioritymode for the algorithm, for improving the selectivity for the object. Incase of the snap photographing mode in which the object is notnecessarily positioned at the center, there are selected the wide AFarea mode and the minimum distance priority→present condition prioritymode for the algorithm, thereby improving the object following abilityand the auto focusing stability. In case of the landscape photographingmode, in which enough time is often available for changing the imageframing with focus locking after focusing with the main object at thecenter, there are selected the center spot mode for the AF area and thecenter priority mode for the algorithm, thereby improving theselectivity for the object. In case of the close-up photographing mode,in which the area of object to be focused is often narrow, there areselected the center spot AF area mode and the center priority mode forthe algorithm, thereby improving the selectivity for the object. In thismanner the selection of the photographing mode according to the objectallows to select the optimum AF area and algorithm for said object.

Also in connection with the selection of the focusing mode by aselecting device 63 as indicated in the left-hand column of Tab. 7,among a single mode (focusing locked after focusing), a continuous mode,a focus tracking mode (correcting lens drive amount for a movingobject), a power focus mode and a manual mode, the AF area and thealgorithm may be respectively selected as shown in the center andright-hand columns. In case of the single focus mode, mostly used for astopped object, there are selected the center spot mode for the AF areaand the center priority mode for the algorithm, thereby improving theselectivity for the object. In case of the continuous focus mode, mostlyused for a moving object, there are selected the wide mode for the AFarea and the minimum distance priority-present condition priority modefor the algorithm, thereby improving the object following ability andthe auto focusing stability. In case of the focus tracking mode, whichis often used for an object moving closer to the camera, there areselected the center spot→wide mode for the AF area and the minimumdistance priority mode for the algorithm, thereby improving the objectselectivity and the object following ability. In case of the power focusmode, in which time for image frame change is not available in mostcases, there are selected the wide AF area and the minimum distancepriority→present condition priority mode for the algorithm, therebyimproving the object following ability. In case of the manual focusmode, which is often used when an exact focusing to a part of the objectis desired, there are selected the center spot mode for the AF area andthe center priority mode for the algorithm, thereby improving the objectselectivity. In this manner the selection of a photographing modeaccording to the object allows to select the AF area and the algorithmoptimum for said object.

In the foregoing there has been explained the switching of the AF areaand algorithm in response to the manual selection of one of variousphotographing modes, but a similar effect can be obtained by theswitching of the AF area and algorithm in connection with an automaticselection of such photographing modes.

The switching of the AF area and algorithm may also be conducted, asshown in FIG. 8, based on the comparison of the time T elapsed from thehalf-stroke depression of a shutter release button 61 and a redeterminedtime T1. If the elapsed time T is shorter than said predetermined timeT1, there are selected the center spot mode for the AF area and theminimum distance priority mode for the algorithm, thus giving emphasisto the object selectivity. If the former is equal to or longer than thelatter, there are selected the wide AF area and the present conditionpriority mode for the algorithm, thus giving emphasis to the objectfollowing ability and the auto focusing stability.

In the following there will be explained embodiments for selecting theAF area and algorithm according to information obtained by variousdetecting devices of the camera itself, instead of selection byselecting devices for the camera operations.

In case information is obtained on the object distance, the AF area andalgorithm may be selected as shown in the center and right-hand columnsin Tab. 9, according to said information. As already known, the objectdistance information can be obtained for example from the de focusamount determined from the focus detection and the absolute position ofthe phototaking lens. When the object distance is short, the object isclosed up, and the focus varies considerably depending on the positionin the image field. Therefore, in order to increase the selectivity forthe object, there are selected the center spot mode for the AF area andthe center priority mode for the algorithm. When the object distance islong, the object appears smaller and more difficult to catch in theimage field, there are selected the wide AF area and the minimumdistance priority-present condition priority mode for the algorithm. Ifthe object distance is medium, there are selected intermediateselections, namely the center spot-wide mode for the AF area and theminimum distance priority-present condition priority mode for thealgorithm. In this manner optimum AF area and algorithm can be selectedaccording to the object distance.

In case information is obtained on the photographing magnification, theAF area and algorithm may be selected as shown in the center andright-hand columns in Tab. 10, according to said information. As alreadyknown, the magnification information can be obtained, for example, fromthe defocus amount determined from focus detection, the absoluteposition of the phototaking lens, and the focal length thereof. When themagnification is large, the object appears large and the focus variesconsiderably depending on the position in the image field. Therefore, inorder to increase the selectivity for the object, there are selected thecenter spot mode for the AF area and the center priority mode for thealgorithm. When the magnification is small, the object appears smallerand more difficult to catch in the image field, there are selected thewide AF area and the minimum distance priority-present conditionpriority mode for the algorithm. If the magnification is medium, thereare selected intermediate selections, namely the center spot-wide modefor the AF area and the minimum distance priority-present conditionpriority mode for the algorithm. In this manner optimum AF area andalgorithm can be selected according to the photographing magnification.

In case information is obtained on the focal length, the AF area andalgorithm may be selected as shown in the center and right-hand columnsin Tab. 11, according to said information. As already known, the focallength information can be obtained, for example, from the lensinformation sent from the lens CPU 12. In a macro mode the objectappears large and the focus varies considerably depending on theposition in the image field. Therefore, in order to increase theselectivity for the object, there are selected the center spot mode forthe AF area and the center priority mode for the algorithm. For a shortfocal length, the object appears smaller and more difficult to catch inthe image field, there are selected the wide AF area and the minimumdistance priority-present condition priority mode for the algorithm. Fora long focal length, there are made intermediate selections, namely thecenter spot-wide for the AF area and the minimum distancepriority-present condition priority mode for the algorithm. In thismanner optimum AF area and algorith can be selected according to thefocal length information.

In the above-explained selection of the AF area and the algorithm basedon the object distance, magnification or focal length, the AF area andalgorithm are selected for a smaller area to increase the objectselectivity if the object appears larger in the image field, but for alarger area to facilitate the capture of object if the object appearssmaller in the image field. It is possible also, however, to select theAF area and algorithm for a wider area if the object appears larger inthe image field because the object itself is large already, therebyfacilitating the capture of object and improving the auto focusingstability, and to select the AF area and algorithm for a smaller area ifthe object appears smaller in the image field thereby improving theselectivity for the object.

In case information is obtained on the aperture value, the AF area andalgorithm may be selected as shown in the center and right-hand columnsin Tab. 12, according to said information. As already known, theaperture value information can be obtained from the main CPU 60controlling the aperture control device 83. In case the aperture valueis small, requiring a higher accuracy in focusing, there are selectedthe center spot AF area and the center priority mode for the algorithm,thereby improving the object selectivity. In case the aperture value islarge, where the depth of focus is large and does not require a highaccuracy in focusing, there are selected the wide AF area and theaverage priority mode for the algorithm. In this manner there areselected optimum AF area and algorithm according to the aperture valueinformation.

In case information is obtained on the shutter speed, the AF area andalgorithm may be selected as shown in the center and right-hand columnsin Tab. 13, according to said information. As already known, the shutterspeed information can be obtained from the main CPU 60 controlling theshutter speed control device 82. For a high shutter speed, which isoften used for a moving object, there are selected the wide AF area andthe minimum distance priority-present condition priority mode for thealgorithm, in order to improve the object capturing ability. For a lowshutter speed, often used for a stopped object, there are selected thecenter spot AF area and the center priority-present condition prioritymode for the algorithm, thereby improving the object selectivity. Inthis manner optimum AF area and algorithm can be selected according tothe shutter speed information.

In case information is obtained on the object luminance, the AF area andthe algorithm may be selected as shown in the center and right-handcolumns in Tab. 14, according to said information. As already known, theobject luminance information can be obtained, for example, from theresult of luminance detection by the main CPU 60 based on the output ofthe light metering sensor 86. In case of a high luminance, where theobject can be clearly identified in most cases, there are selected thecenter spot AF area and the center priority mode for the algorithm, thusgiving emphasis on the object selectivity. In case of a low luminance,where the object may not be clearly identifiable, there are selected thewide AF area and the minimum distance priority mode for the algorithm,giving emphasis to the object capturing ability. In this manner optimumAF area and algorithm can be selected according to the object luminanceinformation.

In case information is obtained on the electronic flash, the AF area andthe algorithm may be selected as shown in the center and right-handcolumns in Tab. 15, according to said information. As already known, theelectronic flash information can be obtained by communication with themain CPU 60 controlling the built-in electronic flash unit or with a CPUincorporated in the electronic flash unit. In case the electronic flashis not used, the object is of a high luminance and is clearlyidentifiable in most cases, so that selected are the center spot AF areaand the center priority mode for the algorithm, thereby giving emphasisto the object selectivity. In case the electronic flash is used, theobject is of a low luminance and is not clearly identifiable in mostcases, so that there are selected the wide AF area and the minimumdistance priority mode for the algorithm, thus giving emphasis to theobject capturing ability. In this manner optimum AF area and algorithmcan be selected according to the electronic flash information.

In case information is obtained on the aberrations of the phototakingoptical system, the AF area and the algorithm may be selected as shownin the center and right-hand columns in Tab. 16, according to saidinformation. As already known, the aberration information can beobtained, for example, from the lens information supplied by the lensCPU 12. In case the difference in aberration between the axial andperipheral positions is large (for example a large image planecurvature), there are selected the center spot AF area and the centerpriority mode for the algorithm, because the focus detection on or nearthe axial position provides better accuracy. If said difference issmall, there are selected the wide AF area and the minimum distancepriority-present condition priority mode for the algorithm, since enoughaccuracy can be obtained even by the focus detection in the peripheralarea. In this manner optimum AF area and algorithm can be selectedaccording to the aberration in formation.

In case information is obtained on the camera body position, the AF areaand the algorithm may be selected as shown in the center and right-handcolumns in Tab. 17, according to said information. As already known, thebody position information can be obtained, for example, from a positiondetecting device 69, such as a mercury switch, provided in the camerabody. In case of vertical body position, as the focus detection in thevertical direction has a higher probability of object detection, thevertical photosensor elements shown in FIG. 1 are selected as the AFarea, and the minimum distance priority mode is selected for thealgorithm. In the horizontal body position, as the focus detection inthe horizontal direction has a higher probability of object detection,the horizontal photosensor elements shown in FIG. 1 are selected as theAF area, and the minimum distance priority-present condition prioritymode is selected for the algorithm. In this manner optimum AF area andalgorithm can be selected according to the body position information.

In the following there will be explained embodiments in which the AFarea and the algorithm are selected according to the result of focusdetection or according to the object image data.

In case information is obtained on the object pattern, the AF area andthe algorithm may be selected as shown in the center and right-handcolumns in Tab. 18, according to said information. The object patterninformation can be obtained in the AF calculating CPU 40 itself, forexample by applying the equations (11) to the image data for focusdetection. If the object pattern has a high contrast, the object can beclearly identifiable in most cases, so that there are selected thecenter spot AF area and the center priority mode for the algorithm,giving emphasis to the object selectivity. In case of a low contrast,where the object may not be clearly identifiable, there are selected thewide AF area and the minimum distance priority-present conditionpriority mode for the algorithm, in order to give emphasis to the objectcapturing ability. In this manner optimum AF area and algorithm can beselected according to the object pattern information.

In case information is obtained on the defocus amount, the AF area andthe algorithm may be selected as shown in the center and right-handcolumns in Tab. 19, according to said information. The defocusinformation can be obtained, for example, from the AF calculating CPU 40itself executing the focus detecting calculation. If the defocus amountis small, the object is clearly identifiable in most cases, and there isrequired a limited mutual displacement of the image data in thecorrelation calculation for focus detection. Consequently there areselected the center spot AF area and the center priority mode for thealgorithm, thus giving emphasis to the object selectivity. In case of alarge defocus, where the object is often not clearly identifiable andthe mutual displacement of image data becomes larger in the correlationcalculation for focus detection, there are selected the wide AF area andthe minimum distance priority mode for the algorithm, in order to giveemphasis to the object capturing ability. In this manner optimum AF areaand algorithm can be selected according to the defocus information.

In the foregoing there has been explained the selection of the AF areaand the algorithm in relation to various conditions, but it is alsopossible to alter various discriminating conditions in the AFcalculation according to such conditions. For example, the parametersC(km) and SLOP determined in the equations (6) are capable ofdetermining the reliability of the defocus amount DEF, and can thereforebe used for discriminating whether the focus detection is possible ornot, as shown in the relations (13):

    C(km)>Cs or SLOP<Ss . . . detection impossible

    C(km)=<Cs and SLOP≧Ss . . . detection possible      (13)

Consequently, the discrimination of the status of focus detectionoptimum for said conditions can be realized by varying the values Cs, Ssin (13) in relation to said conditions. More specifically said valuesare selected tightly (smaller Cs and larger Ss) in a state where exactfocus detection is possible or necessary (small AF area; algorithm incenter priority mode or minimum distance priority mode; spot lightmetering mode; aperture value priority AE mode; single film windingmode; portrait photographing mode; single focusing mode; short objectdistance; high photographing magnification; long focal length; smallaperture value; fast shutter speed; high luminance; small difference inaberrations; high contrast; or small defocus amount), and said valuesare selected loosely (larger Cs and smaller Ss) if exact focus detectionis not possible or unnecessary (large AF area; present conditionpriority algorithm mode; multi light metering mode; programmed AE mode;continuous film winding mode; sports photographing mode; continuousfocusing mode; long object distance; small photographing magnification;short focal length; large aperture value; slow shutter speed; lowluminance; large difference in aberrations; low contrast; or large defocus amount) .

It is also possible to vary the reference values Ns, Ws (>Ns) in focusdetecting relations shown in (14), according to the above-mentionedconditions:

|DEF| (not during focusing)>Ns;

|DEF| (during focusing)>Ws . . . not in-focus

|DEF| (not during focusing)≦Ns;

|DEF| (during focusing)≦Ws . . . in-focus

More specifically, said values are selected tightly (smaller Ns and Ws)if exact focus detection is possible or required and emphasis is givento accuracy than to response (small AF area; center priority or minimumdistance priority algorithm mode; spot light metering mode; aperturevalue priority AE mode; single film winding mode; portrait photographingmode; single focusing mode; short object distance; high photographingmagnification; long focal length; small aperture value; fast shutterspeed; high luminance; small difference in aberrations; high contrast;or small defocus amount), and said values are selected loosely (largerNs and Ws) if exact focus detection is not possible or emphasis is givento response than to accuracy (large AF area; present condition priorityalgorithm; multi light metering mode; programmed AE mode; continuousfilm winding mode; sports photographing mode; continuous focusing mode;long object distance; small photographing magnification; short focallength; large aperture value; s low shutter speed; low luminance; largedifference in aberrations; low contrast; or large defocus amount).

It is furthermore possible, in a predicted drive technology disclosed inthe Japanese Patent Application Sho 63-247829 of the present applicant(in which a correction for object movement is added to the lens driveamount in auto focusing by detecting the axial movement of the object),to vary the discriminating reference values for a moving object(parameters α, δ, r and k in steps 450,510 and 515 in FIG. 15 of thespecification of said patent application) according to theabove-mentioned conditions. More specifically, said values are soselected to preclude the predicted drive (larger δ, k and smaller α, r)in case of photographing a stopped object or emphasis being given tostability than to response (small AF area; center priority or minimumdistance priority algorithm mode; spot light metering mode; aperturevalue priority AE mode; single film winding mode; portrait photographingmodel single focusing mode; short object distance; high photographingmagnification; long focal length; small aperture value; slow shutterspeed; low luminance; large difference in aberrations; low contrast; orsmall defocus amount), and said values are selected loosely (smaller δ,k and larger α, r) in case of photographing a moving object of emphasisbeing given to response than to stability (large AF area; presentcondition priority algorithm mode; multi light metering mode; programmedAE mode; continuous film winding mode; sports photographing mode;continuous focusing mode; long object distance; small photographingmagnification; short focal length; large aperture value; fast shutterspeed; high luminance; small difference in aberrations; high contrast;or large defocus amount). Thus, when the tracking mode is selected by afocus mode selecting device 63, the AF calculating CPU 40 discriminatesa moving object and, upon identifying a moving object, adds a correctionfor the moving object to the defocus amount.

[Function of lens drive control CPU]

When the AF calculating CPU 40 determines the final defocus amount anddetects the focus state through the procedure shown in FIG. 27, theinformation on said defocus amount and focusing state (detectionimpossible or in-focus state) is sent to the lens drive control CPU 50shown in FIG. 26. When an AF (single, continuous, or tracking) mode isselected by the selecting device 63, said CPU 50 calculates the lensdrive amount to the in-focus point, based on said defocus amount, anddrives the AF motor 51 in a direction to bring the photographing lens 11toward the in-focus point. The rotation of said AF motor is transmittedthrough a body transmission system 52, composed of gears provided in thecamera body, a clutch B53, a camera body coupling 54 and a lens coupling18 provided at the mounting portions of the camera body 20 and the lens10, and a lens transmission system 13 composed of gears provided in thelens, and finally drives the phototaking lens 11 toward the in-focusposition. The drive amount of the AF motor 51 is converted from therotational amount of gears constituting the body transmission system 52into a pulse train signal by an encoder 55 composed for example of aphotointerruptor, and fed back to the lens drive control CPU 50. SaidCPU 50 detects the drive amount and drive speed of the AF motor 51 bymeasuring the number and interval of said pulses, and controls the AFmotor 51 in such a manner that the lens is stopped exactly at thein-focus position.

When the power focus mode is selected by the focus mode selecting device63, the lens drive control CPU 50 receives the direction, amount andspeed of movement of a distance ring 15 of the lens 10, through anencoder 16 composed for example of a photointerruptor, a lens contact19B and a camera body contact 59B, both provided in the mounting portionof the camera body 20 and the lens 10. Said moving direction can beidentified by generating two signals by monitoring the movement of saidring with a phase difference of 90° and detecting the phase relationshipof said signals. Based on these information, there are determined theamount, speed and direction of lens drive, and the AF motor 51 iscontrolled in a similar manner as in the AF mode, thereby moving thelens 11 corresponding to the movement of the lens distance ring.

In the AF mode and power focusing mode explained above, as the power forlens drive is supplied by the AF motor 51, the lens drive control CPU 50maintains the clutch B53 in coupled state by a clutch control device 56,thereby transmitting the rotation of said motor 51 to the lens, anddisconnects a clutch L14 of the lens 11 through contacts 19A, 59Aprovided in the lens mount portion, thereby preventing the movement ofthe lens distance ring 15 from being transmitted to the lenstransmission system 13. The amount and speed of movement of the lens ismonitored by the encoder 55 which monitors the movement of the lenstransmission system 52, but such method may result in an error becauseof gear backlashes in the relative long transmission path from thecamera body to the lens. In order to avoid this drawback, it is alsopossible to provide an encoder 17 for monitoring the movement of thelens transmission system 13, thereby directly monitoring the movement ofthe lens 11, and to feed thus obtained monitor signal to the lens drivecontrol CPU 50 through the contacts 19C, 59C provided in the lens mountportion thus achieving more exact control on the amount and speed ofmovement of the lens.

When the manual mode is selected by the selecting device 63, as the lensdriving power is supplied by the lens distance ring 15, the lens drivecontrol CPU 50 disconnects the clutch B53 by the control device 56,thereby preventing the rotation of the AF motor 51 from beingtransmitted to the lens, and maintains the clutch L14 of the lens inconnected state through the contacts 19A, 59A of the lens mountingportion, thereby transmitting the rotation of the lens distance ring 15to the lens transmission system 13.

In the foregoing explanation, the power focusing mode and the manualfocusing mode are selected by the focus mode selecting device 63provided on the camera body, but it is also possible to provide a touchsensor device 41, as shown in FIG. 31, for detecting that the distancering 15 is touched by the photographer for focusing of the lens 10, andto switch the focusing mode to the power focusing mode or manualfocusing mode upon detection by said sensor 41 that said distance ring15 is touched or manipulated by the photographer, and to another modeselected by the selecting device 63 in the absence of such detection.Such structure improves the convenience of operation, since, when thephotographer wishes focusing in the power focus mode or manual mode, heneed not to manipulate the selecting device 63 but has only to operatethe distance ring as in the conventional manual focusing operation.

The aforementioned AF modes require exact control the lens drive amount,and such exact control generally necessitates a low drive speed in thevicinity of the in-focus position. The drive speed control of the lensis generally achieved by on/off pulse control of the AF motor 51 and byvarying the duty ratio of-said pulses. Also such speed control can beachieved, as disclosed in the Japanese Laid-open Patent Sho 57-46216 ofthe present applicant, by dividing the deviation from the in-focusposition to the current lens position into a certain number of zones andmaintaining a constant drive speed in each zone. However, in such speedcontrol method in which the speed is gradually reduced stepwise inplural zones, there results unnecessary speed control, eventuallyleading to a long time required to reach the in-focus position.

In general, the stopping characteristics of a motor is represented bythe equations (15), indicating that the revolution of the motordecreases exponentially:

    N(t)=N0×exp(-t/T0)

    Wt=T0×N0                                             (15)

wherein N(t) is the rotating speed of the motor, N0 is the revolution atthe start of braking, t is time, T0 is a time constant, and WT is theamount of rotation from the start of braking to the stopped state.Ideally, therefore, the motor can be stopped, with the applied braking,at the desired stop position if the braking is started when theremaining amount of rotation to said desired stop position becomes equalto WT. Though the behavior of actual lenses differ from the equations(15) for example due to fluctuations in the driving torque, the stoppingat the desired stop position can be achieved within a shortest time by acontrol in which the rotating speed Nr at deceleration is proportionalto the remaining amount Wr of rotation, such as Nr=Wr/T0. In the AFdrive control, the remaining drive amount to the in-focus position canbe determined by subtracting the number of pulses, generated by theencoder 16 or 55 from the start point of braking, from the amount ofdrive (number of pulses) from the braking start position to the in-focusposition, and the drive speed can be determined from the interval ofpulses. FIG. 32 shows the monitor signals in case the braking is appliedat a point with remaining pulses m in front of the in-focus point, tothe AF motor in full speed rotation, for theoretical stopping at thein-focus point. In such case, the in-focus point can be reached within ashort time even in the presence of certain fluctuation in the stoppingcharacteristics, by controlling the AF motor in such a manner that thepulse internal tn at the remaining pulses n is inversely proportional tothe remaining pulses, as shown in the equation (16):

    tn=t0/n                                                    (16)

wherein the time constant t0 is a theoretically determined value foreach lens drive system. Consequently, the remaining pulse number n andthe pulse interval tn are mutually correlated as shown in FIG. 33. Thus,if the pulse interval tn', measured at the remaining pulses n, isshorter or longer than the theoretical pulse interval tn shown in FIG.33, the driving speed is respectively reduced or increased. The drivingspeed can be increased or decreased by varying the on/off duty ratio ofthe drive signal for the AF motor. For example, in drive signals shownin FIG. 34, the drive speed can be varied by increasing or decreasingthe on-time td while maintaining the cycle time tx constant.

In the following there will be explained the function of the lens drivecontrol CPU 50 with reference to FIGS. 35 to 38. Referring to FIG. 35,upon start of power supply, a step S060 discriminates whether the lensposition information is necessary, and, if necessary, a step S065retracts the lens to the end position corresponding to the infiniteobject distance, and, taking said position as the lens reset position,measures the amount of lens advancement from said position by countingthe encoder pulses. If said information is not required, the step S065is omitted. Then a step S070 repeats an operation according to thefocusing mode selected by the selecting device 63. However, if thefocusing mode is varied, the sequence returns to the step S060. In theconventional process, the lens is always retracted even when the lensposition information is not required, so that the photographer has towait until the completion of lens retraction, even if a photographingoperation is desired immediately after the start of power supply. Theabove-explained procedure avoids this drawback, since the lens isretracted only when the lens position information is required (forexample for varying the AE or AF mode or parameters according to thelens position).

FIG. 36 is a flow chart in the AF (single, continuous or tracking) mode.At first a step S080 executes clutch control so as to transmit therotation of the AF motor to the phototaking lens and to disconnect thedistance ring 15 therefrom. Then a step S085 discriminates whether thefocus detection by the AF calculating CPU 40 has provided an in-focusstate, and, if not, a step S090 converts the de focus amount into a lensdrive amount. Then a step S095 drives the lens by the AF motor 51corresponding to said drive amount, and, upon completion of said drive,the sequence returns to the step S085. If the in-focus state isidentified in the step S085, a step S100 discriminates whether thesingle mode has been selected, and, if not, the sequence returns withoutlens drive to the step S085 to await the result of next focus detection.If the single mode has been selected, a step S105 locks the focusingthereby inhibiting the lens drive thereafter, and allows the main CPU 60to release the shutter. The sequence thereafter returns to the step S085in response to the turning-off of the half-stroke depression of theshutter release button 61 or to the shutter operation.

FIG. 37 shows a flow chart in the power focusing mode. A step S110executes the clutch control, thereby transmitting the rotation of the AFmotor 51 to the phototaking lens and disconnecting the distance ring 15therefrom. A step S115 measure the amount and direction of movement ofsaid distance ring 15, then a step S120 converts said amount of movementinto a lens drive amount, and a step S125 drives the lens by the AFmotor 51 corresponding to said drive amount. Thereafter the sequencereturns to the step S115.

FIG. 38 is a flow chart in the manual mode, in which a step S130controls the clutch thereby transmitting the movement of the distancering 15 to the phototaking lens and disconnecting the AF motor 51therefrom.

In the foregoing explanation of the function of the lens drive controlCPU 50, the focusing modes are selected by the focus mode selectingdevice 63. In the following there will be explained embodiments in whichthe focusing modes are not selected by an exclusive selecting device butin relation to the function of a selecting device used for selectingother functions of the camera.

In case the AF area is selected by the selecting device 66 as shown inthe left-hand column of Tab. 20, among the view point detection, centerspot, selected spot, wide, and center spot-wide modes, the focusing modemay be selected in connection, as shown in the right-hand column. Incase of the center spot or selected spot mode for the AF area, which ismostly used for photographing an object stopped in a certain point inthe image field, the single focusing mode is selected to give emphasisto the stability. In case of the view point detection or wide mode forthe AF area, where the object often changes one to another, thecontinuous focusing mode is selected in order to give emphasis toresponse. In case of the center spot→wide mode for the AF area, which ismostly used for a moving object, the tracking focus mode is selected inorder to give emphasis to the object following ability. In this mannerthe AF area and the focusing mode are well matched and there can beimproved the stability and response of auto focusing.

Also in connection with the selection of algorithm by the objectselecting device 67 as shown in the left-hand column of Tab. 21, amongthe center priority, minimum distance priority, average priority→maximumdistance priority, minimum distance priority→present condition priority,and center priority→present condition priority modes, the focusing modemay be selected as shown in the right-hand column. In case of the centerpriority or maximum distance priority mode of the algorithm, which ismostly used for photographing an object stopped at a certain point inthe image field, the single focusing mode is selected in order to giveemphasis to the stability. In the average priority, minimum distancepriority→present condition priority, or center priority→presentcondition priority mode of the algorithm, where the object often changesfrom one to another, the continuous focusing mode is selected in orderto give emphasis to the response. In the minimum distance priority modeof the algorithm, which is mostly used for a moving object, the trackingfocus mode is selected in order to give emphasis to the object followingability. In this manner the algorithm and the focusing mode can be wellmatched, and there can be improved the stability and response of autofocusing.

Also in connection with the selection of the light metering mode by themode selecting device 71 as shown in the left-hand column of Tab. 22,among the center spot, selected spot, partial, center weighted and multimodes, the focusing mode may be selected as shown in the right-handcolumn. In case of the center spot or selected spot light metering mode,which is mostly used for photographing an object stopped at a certainpoint in the image field, there is selected the single focusing mode forgiving emphasis to the stability. In case of the partial or centerweighted light metering mode, where the object may change from one toanother, the continuous focusing mode is selected in order to giveemphasis to the response. In case of the multi light metering mode,mostly used for a moving object, the tracking focus mode is selected forgiving emphasis to the object following ability. In this manner theselection of the light mete ring mode according to the object allows toselect the focusing mode optimum for said object.

Also in connection with the selection of the AE mode by the modeselecting device 70 as shown in the left-hand column of Tab. 23, amongthe aperture priority, shutter speed priority and programmed modes, thefocusing mode may be selected as shown in the right-hand column. In caseof the aperture priority AE mode, often used for photographing an objectstopped in a certain point in the image field, the single focusing modeis selected for giving emphasis to the stability. In case of theprogrammed AE mode, in which the object often changes one to another,the continuous focusing mode is selected for giving emphasis to theresponse. In case of the shutter speed priority AE mode, often used fora moving object, the tracking focus mode is selected for giving emphasisto the object following ability. In this manner the selection of the AEmode according to the object enables to select a focusing mode optimumfor said object.

In case the film winding mode is selected by the mode selecting device65 as shown in the left-hand column of Tab. 24, among the single frame,continuous high-speed, continuous low-speed and selftimer modes, thefocusing mode may be selected as shown in the right-hand column. In caseof the single winding mode, often used for photographing an objectstopped at a certain point in the image field, the single focusing modeis selected for emphasizing the stability. In case of the selftimerwinding mode, in which the object may be added afterwards, thecontinuous focusing mode is selected for giving emphasis to theresponse. In case of the continuous high-speed or continuous low-speedwinding mode, often used for a moving object, the tracking focus mode isselected in order to give emphasis to the object following ability. Inthis manner the selection of the film winding mode according to theobject enables to select a focusing mode optimum for said object.

Also in connection with the selection of the photographing mode by themode selecting device 64 as shown in the left-hand column of Tab. 25,among the sports, portrait, snap, landscape and closeup modes, thefocusing mode may be selected as shown in the right-hand column. In caseof the portrait or landscape photographing mode, which is often used forphotographing an object stooped at a certain point in the image field,the single focusing mode is selected for giving emphasis to thestability. In case of the snap or closeup photographing mode, in whichthe object often changes from one to another, the continuous focusingmode is selected for giving emphasis to the response. In case of thesports photographing mode, mostly used for a moving object, the trackingfocus mode is selected in order to give emphasis to the object followingability. In this manner the selection of the photographing modeaccording to the object enables to select a focusing mode optimum forsaid object.

In the foregoing there has been explained the switching of the focusingmode in response to the manual selection of various modes forphotographing, but a similar effect can also be obtained in case ofautomatic switching of such various modes for photographing, byswitching the focusing mode in response.

Furthermore, the focusing mode may be switched based on the comparisonof the time T, elapsed from the start of half-stroke depression of theshutter release button 61, with a predetermined time T1. In such case,if the elapsed time T is shorter than the predetermined time T1, thecontinuous or tracking focusing mode is selected, emphasizing theresponse to the moving object, and, if the former is longer, the singlefocusing mode is selected in consideration of the stability of autofocusing.

In the following there will be explained embodiments in which thefocusing mode is selected not in relation to the operation of aselecting device of the camera but according to the result of detectionby various detecting devices provided on the camera itself.

In case information is obtained on the object distance, the focusingmode may be selected as shown in the right-hand column of Tab. 27,according to said information. As already known, the object distanceinformation can be obtained, for example, from the defocus amount as theresult of focus detection and the absolute position of the phototakinglens. In case of a short object distance, which is often used forphotographing an object stopped at a certain point in the image field,the single focusing mode is selected for giving emphasis to thestability. In case of a medium object distance, where the object oftenvaries from one to another, the continuous focusing mode is selected forgiving emphasis to the response. In case of a long object distance, inwhich the object is often moving, the tracking focus mode is selectedfor giving emphasis to the object following ability. In this manner thefocusing mode can be selected according to the object distance.

In case information is obtained on the photographing magnification, thefocusing mode may be selected as shown in the right-hand column of Tab.28, according to said information. In case of a large magnification,which is often used for photographing an object stopped at a certainpoint in the image field, the single focusing mode is selected forgiving emphasis to the stability. In case of a medium magnification,where the object often changes from one to another, the continuousfocusing mode is selected for giving emphasis to the response. In caseof a small magnification, in which the object is often moving, thetracking focus mode is selected for giving emphasis to the objectfollowing ability. In this manner the focusing mode can be selectedaccording to the photographing magnification.

In case information is obtained on the focal length, the focusing modemay be selected as shown in the right-hand column of Tab. 29, accordingto said information. In case of a short focal length, which is oftenused for photographing a stopped object such as a landscape, the singlefocusing mode is selected for giving emphasis to the stability. In caseof a long focal length, which is often used for a moving object, thecontinuous or tracking focus mode is selected for emphasizing theresponse. In case of a macro focal length, where the point to be focusedoften varies according to the intention of the photographer, the manualor power focusing mode is selected, thereby giving emphasis to theselectivity of object. In this manner an optimum focusing mode can beselected according to the focal length.

In case information is obtained on the aperture value, the focusing modemay be selected as shown in the right-hand column of Tab. 30, accordingto said information. In case of a small aperture value, which is oftenused for photographing a stopped object such as a landscape or a person,the single focusing mode is selected thereby giving emphasis to thestability. In case of a large aperture value, often used for a movingobject, the continuous or tracking focus mode is selected, in order togive emphasis to the response. In this manner an optimum focusing modecan be selected according to the aperture value information.

In case information is obtained on the shutter speed, the focusing modemay be selected as shown in the right-hand column of Tab. 31, accordingto said information. In case of a low shutter speed, which is mostlyused for photographing a stopped object such as a landscape or a person,the single focusing mode is selected thereby giving emphasis to thestability. In case of a high shutter speed, which is mostly used for amoving object, the continuous or tracking focus mode is selected, givingemphasis to the response. In this manner an optimum focusing mode can beselected according to the shutter speed information.

In case information is obtained on the object luminance, the focusingmode may be selected as shown in the right-hand column of Tab. 32,according to said information. In case of a low luminance, which isoften encountered in photographing a stopped object such as a landscapeor a person, the single focusing mode is selected in order to giveemphasis to the stability. In case of a high luminance, oftenencountered in photographing a moving object, the continuous or trackingfocusing mode, thereby giving emphasis to the response. In this manneran optimum focusing mode can be selected according to the luminanceinformation.

In case information is obtained on the use of electronic flash, thefocusing mode may be selected as shown in the right-hand column of Tab.33, according to said information. In case of electronic flash emission,which is often used for photographing a stopped object such as a person,the single focusing mode is selected in order to give emphasis to thestability. In case of absence of electronic flash emission, where theobject is often moving, there is selected the continuous or trackingfocusing mode in order to give emphasis to the response. In this manneran optimum focusing mode can be selected acording to the electronicflash information.

In case information is obtained on the aberrations of the phototakingoptical system, the focusing mode may be selected as shown in theright-hand column of Tab. 34, according to said information. In case ofa large difference between the axial and peripheral aberrations, whichis unsuitable for photographing with an AF mode, the manual or powerfocusing mode is selected. In case of a small difference, which issuitable for photographing with an AF mode, the single, continuous ortracking focusing mode is selected. In this manner an optimum focusingmode can be selected according to the aberration information.

In the following there will be explained embodiments in which thefocusing mode is selected according to the result of focus detection orthe image data.

In case information is obtained on the focus state, the focusing modemay be selected as shown in the right-hand column of Tab. 35, accordingto said information. Before the in-focus state is reached, the singlefocusing mode is selected for executing photographing with an AF mode.After the in-focus state is reached, the manual or power focusing modeis selected in order to enable a fine focus adjustment by thephotographer. In this manner an optimum focusing mode can be selectedaccording to the focus state information.

In case information is obtained on the detection propriety, the focusingmode may be selected as shown in the right-hand column of Tab. 36,according to said information. In case the focus detection is possible,the single or continuous focusing mode is selected in order to enablephotographing with an AF mode. In case the focus detection isimpossible, the manual or power focusing mode is selected in order toenable focusing by the photographer. In this manner an optimum focusingmode can be selected according to the information on detectionpropriety.

In case information is obtained on the objected pattern, the focusingmode may be selected as shown in the right-hand column of Tab. 37,according to said information. In case of a low object contrast, whichis unsuitable for photographing a moving object, the single focusingmode is selected in order to give emphasis to the stability. In case ofa high contrast, which is suitable for photographing a moving object,the continuous or tracking focusing mode is selected in order to giveemphasis to the response. In this manner an optimum focusing mode can beselected according to the object pattern in formation.

In case information is obtained on the defocus amount, the focusing modemay be selected as shown in the right-hand column of Tab. 38, accordingto said information. In case of a large defocus amount, the continuousfocusing mode is selected, giving emphasis to the response. In case of asmall defocus amount, the single focusing mode is selected givingemphasis to the stability. In this manner an optimum focusing mode canbe selected according to the defocus information.

[Function of main CPU]

Referring to FIG. 26, the camera body 20 incorporates a main CPU 60 formainly controlling the camera sequence and the exposure operation. Saidmain CPU 60 obtains the object luminance from a light metering sensor 86and exposure setting information such as film sensitivity, aperturevalue, shutter speed etc. from unrepresented setting devices, determinesthe aperture value and the shutter speed based on these information, anddisplays these information on a display device 85. In the photographingoperation, it also controls the up-down movement of a main mirror 21 bya mirror control device 81, the function of a diaphragm aperturemechanism by an aperture control device 83 and the function of a shuttermechanism by a shutter control device 82. Also after the photographingoperation, it controls the function of a film winding-charging mechanismby a winding-charging control device 84, in preparation for the nextphototaking operation. The main CPU 60 is also linked with variouscamera operation device 80, lens CPU 12, lens drive control CPU 50, AFcalculating CPU 40 and AF detection system controlling CPU 33, thusreceiving information necessary for the camera sequence and the exposurecontrol from other CPU's and sending camera sequence information toother CPU's. For example, in case the single focusing mode is selected,the shutter releasing operation is controlled by a release enablinginstruction supplied from the lens drive control CPU 50.

Also the main CPU 60 is connected with the AF detection systemcontrolling CPU 33 and the memory 34, so that the object luminanceinformation can be obtained not only from the exclusive light meteringsensor 86 but also from the image data used for focus detection and thecharge accumulating time of the photoelectric converting device. Forexample the object luminance can be determined from Bv/Tv, wherein Bv isthe average value of data in an image area used for light metering, andTv is the charge accumulating time.

The object image area used for light mete ring can be selected asfollows. For example, the areas shown in FIG. 29A or 29B may be used aslight metering areas, according to the operation of the AF areaselecting device 66 or the function of the view point detecting device68. In this manner the AF area always coincides with the light meteringarea, so that the focus and exposure can be optimized to a same object.Also in case a loss in the peripheral light amount is detected by the AFdetection system controlling CPU 33 or the AF calculating CPU 40,whereby the image data area used for focus detection is limited, theimage data area to be used for light metering may be limitedaccordingly.

[Function of image display control CPU]

Referring to FIG. 26, the camera body 20 also incorporates an imagedisplay control CPU 90 for controlling the information display relatingto focus detection. Said CPU 90 obtains focus detection information(focus detection area, selected point, in-focus/out-of-focus, focusingdirection etc.) from the AF calculating CPU 40 and displays saidinformation on a display device 92. The display may be manually turnedon or off by a display selecting device 91.

The display device 92 may also be turned on or off in relation to theoperation of other devices. For example, the display device 92 isautomatically turned off when the manual mode is selected by the focusmode selecting device 63. In this manner the photographer can turn offthe display if it is unnecessary. The display device 92 is composed ofan electrooptical device and transparent electrodes, such as anelectrochromic device or an electroluminescence device, positioned on aplane, conjugate with the film plane, in the view finder. For examplethe wide or spot focus detection area is displayed within the imagefield,

as shown in FIGS. 39A and 39B. As explained in the foregoing, the focusdetection area is selected according to the result of detection by thelight amount distribution detecting device, or according to theoperation of the AF area selecting device 66 or other operating devices.Also in case plural focus detection areas are set within the image fieldby the AF area selecting device 66 or the view point detecting device68, the areas finally selected by the AF calculating CPU 40 aredisplayed as shown in FIG. 40C.

The focus detection states (in-focus or out-of-focus) are displayed asshown in FIGS. 40A to 40F. In an embodiment shown in FIG. 40A, the framealone of the distance measuring area is displayed in the out-of-focusstate, and in the in-focus state, the interior of said frame is changedto semi-transparent to indicate the in-focus state. As variations ofsaid display, the color of the interior may be changed between thein-focus and out-of-focus states, or may be changed according to thedirection of defocus in the out-of-focus state. In an embodiment shownin FIG. 40B, the frame of the distance measuring area is displayedthinner and thickers, respectively in the out-of-focus state and in thein-focus state. As variations of said display, the color of said framemay be changed between the in-focus and out-of-focus states, or may bechange according to the direction of defocus in the out-of-focus state.In an embodiment shown in FIG. 40C, said frame is displayed in brokenlines or solid lines respectively in the out-of-focus and in-focusstates. In FIG. 40D, said frame is displayed in a form of parentheses ora rectangular form, respectively in the out-of-focus and in-focusstates. In FIG. 40E, said frame is displayed only in the out-of-focusstate, and is not displayed in the in-focus state. This mode of displayimproves the convenience of operation, since the focus detection area isdisplayed only when the object is to be selected, and the image fieldbecomes easier to watch after the in-focus state is reached, by thedisappearance of the frame. In case of FIG. 40F, in the out-of-focusstate, a part of the rectangular frame is cut off, and the amount anddirection of defocus are indicated by the position of said cut-offportion. In the in-focus state the rectangular frame is displayedentirely. The display of focus detection information in the image fieldas explained above allows the photographer to constantly watch theobject, without the necessity of looking at another display outside theimage field, so that the photographer can confirm the focus detectioninformation while tracking even a moving object.

In case the display device 92 is provided on the screen 23, while thelight metering sensor 86 is positioned in the view finder and measuresthe light transmitted by said screen 23, the light metering may beaffected by the function state of the display device 92. For avoidingsuch influence, the functions of said display device 92 and said sensoralternated on time-sharing basis. The period of said alternation isselected as 100 ms or shorter, in consideration of human visualcharacteristics, so that the display does not appear flickering.

Also the display device 92 may be constructed as shown in FIG. 41, inorder to avoid the influence of the display on the light mete ringsensor. In FIG. 41, a display device 93, illuminated by an illuminatingdevice 94, is projected to an eye 97 of the observer through a lens 95,and a half mirror 96 provided in the eyepiece lens 25. The shapes andpositions of said optical components are so selected that the displayface of the display device 93 overlaps with the image field of the viewfinder. In the displays shown in FIGS. 40A to 40F, the display face ispositioned substantially conjugate with the surface of the screen inorder to display the focus detection area, but, if an in-focus displayalone is required, the optical system may be simplified without saidconjugate relationship and may be so constructed as to project the lightfor example of a light-emitting diode toward the eye of the observer.Such structure also saves the space in the view finder.

The structure shown in FIG. 26 is designed to observe an optical objectimage in the view finder, but a structure for observing an object imagedisplayed by a display device 98 based on electrical signals, as shownin FIG. 42, allows the synthesis of the object image and the AFinformation relatively easily.

Referring to FIG. 42, in a state where the lens 10 is mounted on thecamera body 20, a light beam from the object is transmitted by thephototaking lens 11 and a reduction optical system 99 insertable intothe optical path in the camera body 20, then reflected by a mirror 100and guided, as a light beam for focus detection and observation, to theaforementioned focus detecting optical system 30. Said reduction opticalsystem 99 is provided to reduce the image size, after passing the focusdetecting optical system 30, to the photosensor area of thetwo-dimensional photoelectric converting device 32 for auto focusing,and is retracted, together with the mirror 100, from the light path bythe AF detection system control CPU 33, at the exposure of the film. Theimage data of plural pairs obtained in the photoelectric convertingdevice 32 are stored in the memory 34, then read by the image displaycontrol CPU 90, and, after the synthesis of AF information by said CPU90, displayed on the image display device 98 for observation through theeyepiece lens 25. For example the focus detecting optical system shownin FIG. 16 provides a pair of two-dimensional image data, but thedisplayed data may be either of said pair, or synthesized from both ofsaid pair, or switched between both of said pair. Display with either ofsaid paired data facilitates observation of the object because the imageis not blurred much even in the out-of-focus state, but display withsynthesized data is convenient for confirming the state of image blurbecause the state of blur is close to that in the actual photograph.Also the image magnification on the display device 98 can be varied bymoving a part of the reduction optical system 99 under the control ofthe AF detection system control CPU 33, and such performance isconvenient for focus detection or observation of an enlarged part of theobject without change in the phototaking optical system 11.

In the foregoing embodiment, the display device 98 is incorporated inthe camera body 20. In the following there will be explained anembodiment for image display outside the body, with reference to FIG.43.

In FIG. 43, image data synthesized from the object image data and the AFdisplay information in the image display control CPU 90 are displayed,through a coupling device B202 for connecting the body 20 with anexternal device, on an external image display device 200 such as aliquid crystal display. Said coupling device B202 may be with wires orwireless. Such structure allows to observe the object image and the AFstate without the camera body 20 at hand, and therefore expands thephotographing situations in combination with an unrepresented remotecontrol unit. Also the object image data fetched by the image displaycontrol CPU 90 may be stored in an external image memory device 201 suchas a memory card, through a coupling device A203 for coupling the body20 with an external device.

In the above-explained structures, as the image data used forobservation or storage are same as those for split-pupil focus detectionobtained by the auto focusing photoelectric converter, a samephotoelectric converting device can be used for both purposes. Thus suchstructures are very advantageous in cost and in space.

Also in the focus detecting device shown in FIG. 26, the presence of AFdetection system control CPU 33, AF calculating CPU 40, lens drivecontrol CPU 50 and image display control CPU 90 in independent mannerallows to execute the control of the photoelectric converting device,focus detecting calculation, lens drive control and display control inmutually overlapping manner in time, thereby improving the response ofthe focus detecting operation.

In the following explained is another embodiment of the focus detectingdevice, with a modified focus detecting optical system.

FIG. 44 is a block diagram of a focus detecting device employing, as thesplit-pupil focus detecting optical system, an optical system in which aphysical diaphragm 450 composed of an electrooptical device such as anelectrochromic device in the light path of the phototaking opticalsystem 11, thereby effecting mechanical pupil splitting in front of theprimary image plane without the refocusing in the optical system in FIG.1, wherein same components as those in FIG. 26 are omitted for thepurpose of simplicity.

FIG. 45 is a perspective view of said focus detecting optical systemalone, wherein a physical diaphragm 450 forms focus detecting pupils305A, 305B, and light beams passing through said pupils are transmittedby a reduction optical system 99 and form object images on aphotoelectric converting device 32, having a two-dimensional photosensorarea 304D positioned equivalent to the film plane. In such opticalsystem, the pupils 305A, 305B are alternately switched on time-dividedbasis by the physical diaphragm 450, and a pair of image signalsobtained from the photoelectric converting device 32 respectivelycorresponding to thus switched pupils 305A, 305B are subjected to thefocus detecting calculation in a similar manner as explained in theforegoing, thereby determining the defocus amount of the phototakinglens 11.

Referring to FIG. 44, in a state where the lens 10 is mounted on thecamera body 20, a light beam from the object is transmitted by aphysical diaphragm 450 provided in the phototaking lens 11 and areduction optical system 99 insertable into the optical path in thecamera body 20, then reflected by a mirror 100 and guided, as a lightbeam for focus detection, to a photoelectric converting device 32positioned on a plane conjugate with the film plane. Said physicaldiaphragm 450 is provided for switching the focus detecting pupils ontime-divided basis, and is so constructed as to switch the form ofaperture as shown in FIGS. 46A and 46B on time-divided basis and tofunction as an ordinary phototaking diaphragm with a selected aperturevalue at the exposure to the film, under the control of the AF detectionsystem controlling CPU 33 through a lens contact 19F and a body contact59F provided in the mounting portion of the camera body 20 and the lens10. Also the information on the form and position of the focus detectingpupils 305A, 305B of the physical diaphragm 450 at the auto focusingoperation is transmitted from the lens CPU 12 to the camera body 20, foruse in the detection of vignetting or in the focus detectingcalculation. The reduction optical system 99 is provided for matchingthe image size with the size of the two-dimensional photosensor area ofthe photoelectric converting device 32 for auto focusing, and, isretracted, together with the mirror 100, from the optical path at theexposure to the film, under the control by the AF detection systemcontrolling CPU 33. It is to be noted that said reduction optical system99 is not an essential component.

The photosensor area 304D of the photoelectric converting device 32 isconstructed, for example, as shown in FIG. 47A.

Referring to FIGS. 47A to 47E, charges generated in a photoelectricconverting element array 500, composed for example of photodiodes, aretemporarily stored, through gates 501, 502, in charge accumulatingelement array 503,504, then transferred through gates 505, 506 to chargetransfer units 507 composed for example of CCD's, and are released fromthe device 32 by the function of said charge transfer units 507.

In the following there will be explained the function of the focusdetecting device shown in FIG. 47A, employing the photoelectricconverting device 32 of a structure shown in FIG. 44, with reference totiming charts shown in FIGS. 48A to 48C and potential charts in FIGS.47B to 47E, illustrating the potential structure of the photoelectricconverting device 32.

In the processing of paired image signals obtained from thephotoelectric converting device 32 in synchronization with the switchingof the focus detecting pupils 305A, 305B controlled on time-dividedbasis by the physical diaphragm 450, a pair only of said image signalsmay result in an error in the focus detection for an object changing intime, such as a moving object, because such paired image signals are notobtained simultaneously. However, the simultaneous character of suchpaired image signals can be improved by inserting, during the chargeaccumulating time of the photoelectric converting device 32 shown inFIG. 48C, plural phases P1 and P2 alternately as shown in FIGS. 48A and48B. During the phases P1 shown in FIG. 48A, the focus detecting pupil305A is selected by the physical diaphragm 450 as shown in FIG. 46A andthe potential of the gate 501 is lowered as shown in FIG. 47B toaccumulate the charges generated in the photoelectric converting elementarray 500 in the charge accumulating array 503. In this state thepotentials of the gates 502, 505 and 506 are selected high. Also duringthe phases P2 shown in FIG. 48B, the focus detecting pupil 305B isselected by the physical diaphragm 450 as shown in FIG. 46B and thepotential of the gate 502 is lowered as shown in FIG. 47C to accumulatethe charges generated in the array 500 in the charge accumulating array504. In this state the potentials of the gates 503, 505 and 506 areselected high.

After repeating the phases P1 and P2 plural times, the chargeaccumulation is terminated and charge reading phases P3 and P4 areinitiated. During said phase P3, the potential of the gate 505 islowered to transfer the charges accumulated in the charge accumulatingelement array 507 to the charge transfer unit 507 in parallel manner.Subsequently the charges are transferred to the exterior by the functionof said charge transfer unit 507. The phase P4 is initiated when thephase P3 is terminated by the completion of transfer of all the charges,accumulated in the array 503, by the function of the charge transferunit 507. In the phase P4, the potential of the gate 506 is lowered totransfer the charges accumulated in the charge accumulating elementarray 504 to the charge transfer unit 507 in parallel manner.Subsequently the charges are transferred to the exterior by the functionof said charge transfer unit 507. An accumulation-readout cycle iscompleted by the termination of the phase P4, upon completion oftransfer of all the charges, accumulated in the array 504, by thefunction of the charge transfer unit 507.

The high-speed switching of the pupils 305A, 305B by the physicaldiaphragm 450 and of the gates of the photoelectric converting device 32in the course of the accumulating time inevitably generates crosstalks(leakage of light beam or charge) between the image signals. Based onthe ideal paired image signals f(x, y), g(x, y) free of such crosstalk,the paired image signals F(x, y), G(x, y) involving such crosstalks canbe represented by the equations (17):

    F(x, y)=a×f(x, y)+b×g(x, y)

    G(x, y)=b×f(x, y)+a×g(x, y)                    (17)

wherein a and b are constants and can be known by measurements inadvance. Consequently, by modifying the equations (17), there can bedetermined the image signals f(x, y), g(x, y) free of crosstalksaccording to the equation (18):

    f(x, y)={b×F(x, y)-a×G(x, y)}/(b-a)

    g(x, y)={a×F(x, y)-b×G(x, y)}/(a-b)            (18)

The focus detecting calculation can be conducted in the same manner asexplained in the foregoing, based on thus obtained paired image signalfree from crosstalks.

As explained in the foregoing, the focus detecting device shown in FIG.44, employing a split-pupil optical system without reimaging as thefocus detecting optical system, does not require a space in the camerabody for focus detection, thereby allowing the compactization of thecamera body and the cost reduction. Also the space in the lens can besaved as the physical diaphragm is used both for the AF diaphragm andthe phototaking diaphragm.

As explained in the foregoing, the focus detecting device of the presentinvention is capable appropriately processing the object image signalsbased on the shape and position of the diaphragms in and the loss inperipheral light amounts in the phototaking optical system and in thefocus detecting optical system, thereby, for example, limiting the areaof or correcting the image signal to be employed in the focus detectingcalculation, whereby the focus detection can be achieved withoutundesirable influence even if the peripheral light amount issignificantly lowered to a level that would normally affect the focusdetecting operation.

                  TABLE 1                                                         ______________________________________                                        AF Area Selection                                                             AF Area         Algorithm                                                     ______________________________________                                        Viewpoint Detection                                                                           Average Priority                                              Center Spot     Center Priority                                               Selected Spot   Average Priority                                              Center Spot → Wide                                                                     Minimum Focusing Priority →                                            Present Condition Priority                                    Wide            Minimum Focusing Priority →                                            Present Condition Priority                                    Horizontal      Minimum Focusing Priority →                                            Present Condition Priority                                    Vertical        Minimum Focusing Priority                                     ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Af Object Selection                                                           AF Area         Algorithm                                                     ______________________________________                                        Center Spot     Center Priority                                               Center Spot     Minimum Focusing Priority                                     Center Spot → Wide                                                                     Center Priority →                                                      Present Condition Priority                                    Wide            Minimum Focusing Priority →                                            Present Condition Priority                                    Wide            Average Priority                                              Wide            Maximum Focusing Priority                                     ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                        Light Metering Mode                                                           Mode      AF Area     Algorithm                                               ______________________________________                                        Center Spot                                                                             Center Spot Center Priority                                         Selected Spot                                                                           Selected Spot                                                                             Minimum Focusing Priority                               Partial   Center Spot →                                                                      Center Priority →                                          Wide        Present Condition Priority                              Center    Center Spot →                                                                      Center Priority →                                Weighted  Wide        Present Condition Priority                              Multi     Wide        Minimum Focusing Priority →                                            Present Condition Priority                              ______________________________________                                    

                  TABLE 4                                                         ______________________________________                                        AE Mode                                                                       Mode      AF Area     Algorithm                                               ______________________________________                                        Aperture  Center Spot →                                                                      Center Priority →                                Priority  Wide        Present Condition Priority                              Shutter Speed                                                                           Wide        Minimum Focusing Priority                               Priority                                                                      Programmed                                                                              Wide        Minimum Focusing Priority →                                            Present Condition Priority                              ______________________________________                                    

                  TABLE 5                                                         ______________________________________                                        Film Winding Mode                                                             Mode      AF Area     Algorithm                                               ______________________________________                                        Single Frame                                                                            Center Spot Center Priority                                         Continuous                                                                              Wide        Minimum Focusing Priority →                      High Speed            Present Condition Priority                              Continuous                                                                              Center Spot →                                                                      Minimum Focusing Priority →                      Low Speed Wide        Present Condition Priority                              Self-Timer                                                                              Wide        Minimum Focusing Priority                               ______________________________________                                    

                  TABLE 6                                                         ______________________________________                                        Photographing Mode                                                            Mode     AF Area     Algorithm                                                ______________________________________                                        Sports   Wide        Minimum Focusing Priority →                                            Present Condition Priority                               Portrait Center Spot Minimum Focusing Priority                                Snap     Wide        Minimum Focusing Priority →                                            Present Condition Priority                               Landscape                                                                              Center Spot Center Priority                                          Close-Up Center Spot Center Priority                                          ______________________________________                                    

                  TABLE 7                                                         ______________________________________                                        Focus Mode                                                                    Mode      AF Area     Algorithm                                               ______________________________________                                        Single    Center Spot Center Priority                                         Continuous                                                                              Wide        Minimum Focusing Priority →                                            Present Condition Priority                              Focus Tracking                                                                          Center Spot →                                                                      Minimum Focusing Priority                                         Wide                                                                Power Focus                                                                             Wide        Minimum Focusing Priority →                                            Present Condition Priority                              Manual    Center Spot Center Priority                                         ______________________________________                                    

                  TABLE 8                                                         ______________________________________                                        Passing Time After Lightly Pressing ON                                        Passing Time                                                                            AF Area     Algorithm                                               ______________________________________                                        T < T1    Center Spot Minimum Focusing Priority                               T1 ≦ T                                                                           Wide        Present Condition Priority                              ______________________________________                                    

                  TABLE 9                                                         ______________________________________                                        Film-to-Object Distance Information                                           Film-to-Object                                                                Distance  AF Area     Algorithm                                               ______________________________________                                        Short Distance                                                                          Center Spot Center Priority                                         Middle    Center Spot →                                                                      Center Priority →                                          Wide        Present Condition Priority                              Long Distance                                                                           Wide        Minimum Focusing Priority →                                            Present Condition Priority                              ______________________________________                                    

                  TABLE 10                                                        ______________________________________                                        Magnification Information                                                     Magnification                                                                           AF Area     Algorithm                                               ______________________________________                                        Large     Center Spot Center Priority                                         Middle    Center Spot →                                                                      Center Priority →                                                      Present Condition Priority                              Small     Wide        Minimum Focusing Priority →                                            Present Condition Priority                              ______________________________________                                    

                  TABLE 11                                                        ______________________________________                                        Focal Length Information                                                      Focal Length                                                                            AF Area     Algorithm                                               ______________________________________                                        Macro     Center Spot Center Priority                                         Short     Wide        Minimum Focusing Priority →                                            Present Condition Priority                              Long      Center Spot →                                                                      Center Priority →                                          Wide        Present Condition Priority                              ______________________________________                                    

                  TABLE 12                                                        ______________________________________                                        Aperture Value                                                                             AF Area      Algorithm                                           ______________________________________                                        Small        Center Spot  Center Priority                                     Large        Wide         Average Priority                                    ______________________________________                                    

                  TABLE 13                                                        ______________________________________                                        Shutter Speed Information                                                     Shutter Speed                                                                           AF Area     Algorithm                                               ______________________________________                                        High Speed                                                                              Wide        Minimum Focusing Priority →                                            Present Condition Priority                              Low Speed Center Spot Center Priority →                                                      Present Condition Priority                              ______________________________________                                    

                  TABLE 14                                                        ______________________________________                                        Luminance Information                                                         Luminance  AF Area    Algorithm                                               ______________________________________                                        High Luminance                                                                           Center Spot                                                                              Center Priority                                         Low Luminance                                                                            Wide       Minimum Focusing Priority                               ______________________________________                                    

                  TABLE 15                                                        ______________________________________                                        Electronic Flash Information                                                  Electronic Flash                                                                         AF Area    Algorithm                                               ______________________________________                                        Emission   Wide       Minimum Focusing Priority                               No Emission                                                                              Center Spot                                                                              Center Priority                                         ______________________________________                                    

                  TABLE 16                                                        ______________________________________                                        Aberration Information                                                        Difference                                                                    Between Axial                                                                 and Peripheral                                                                           AF Area    Algorithm                                               ______________________________________                                        Large      Center Spot                                                                              Center Priority                                         Small      Wide       Minimum Focusing Priority →                                            Present Condition Priority                              ______________________________________                                    

                  TABLE 17                                                        ______________________________________                                        Body Position Information                                                     Vertical Position/                                                            Horizontal Position                                                                       AF Area   Algorithm                                               ______________________________________                                        Vertical Position                                                                         Vertical  Minimum Focusing Priority                               Horizontal Position                                                                       Horizontal                                                                              Minimum Focusing Priority →                                            Present Condition Priority                              ______________________________________                                    

                  TABLE 18                                                        ______________________________________                                        Object Pattern Information                                                    Contrast AF Area     Algorithm                                                ______________________________________                                        High     Center Spot Center Priority                                          Low      Wide        Minimum Focusing Priority →                                            Present Condition Priority                               ______________________________________                                    

                  TABLE 19                                                        ______________________________________                                        Defocus Information                                                           Defocus   AF Area     Algorithm                                               ______________________________________                                        Small     Center Spot Present Condition Priority                              Large     Wide        Minimum Focusing Priority                               ______________________________________                                    

                  TABLE 20                                                        ______________________________________                                        AF Area Selection                                                             AF Area              Focus Mode                                               ______________________________________                                        Viewpoint Detection  Continuous                                               Center Spot          Single                                                   Selected Spot        Single                                                   Center Spot → Wide                                                                          Focus Tracking                                           Wide                 Continuous                                               ______________________________________                                    

                  TABLE 21                                                        ______________________________________                                        AF Object Selection                                                           Algorithm             Focus Mode                                              ______________________________________                                        Center Priority       Single                                                  Minimum Focusing Priority                                                                           Focus Tracking                                          Center Priority →                                                                            Continuous                                              Present Condition Priority                                                    Minimum Focusing Priority →                                                                  Continuous                                              Present Condition Priority                                                    Average Priority      Continuous                                              Maximum Focusing Priority                                                                           Single                                                  ______________________________________                                    

                  TABLE 22                                                        ______________________________________                                        Light Metering Mode                                                           Mode                Algorithm                                                 ______________________________________                                        Centre Spot         Single                                                    Selected Spot       Single                                                    Partial             Continuous                                                Centre Weighted     Continuous                                                Multi               Focus Tracking                                            ______________________________________                                    

                  TABLE 23                                                        ______________________________________                                        AE Mode                                                                       Mode                Focus Mode                                                ______________________________________                                        Aperture Priority   Single                                                    Shutter             Focus Tracking                                            Speed Priority                                                                Programmed          Continuous                                                ______________________________________                                    

                  TABLE 24                                                        ______________________________________                                        Film Winding Mode                                                             Mode                Focus Mode                                                ______________________________________                                        Single              Single                                                    Continuous High     Focus Tracking                                            Speed                                                                         Continuous Low      Focus Tracking                                            Speed                                                                         Self-Timer          Continuous                                                ______________________________________                                    

                  TABLE 25                                                        ______________________________________                                        Photographing Mode                                                            Mode               Focus Mode                                                 ______________________________________                                        Sports             Focus tracking                                             Portrait           Single                                                     Snap               Continuous                                                 Landscape          Single                                                     Close-up           Continuous                                                 ______________________________________                                    

                  TABLE 26                                                        ______________________________________                                        Passing Time After Lightly Pressing ON                                        Passing Time T  Focus Mode                                                    ______________________________________                                        T < T1          Continuous/Focus Tracking                                     T1 ≦ T   Single                                                        ______________________________________                                    

                  TABLE 27                                                        ______________________________________                                        Film-to-Object Distance Information                                           Film-To-Object                                                                Distance            Focus Mode                                                ______________________________________                                        Short Distance      Single                                                    Middle              Continuous                                                Long Distance       Focus Tracking                                            ______________________________________                                    

                  TABLE 28                                                        ______________________________________                                        Magnification Information                                                     Magnification       Focus Mode                                                ______________________________________                                        Large               Single                                                    Middle              Continuous                                                Small               Focus Tracking                                            ______________________________________                                    

                  TABLE 29                                                        ______________________________________                                        Focal Length Information                                                      Focal Length    Focus Mode                                                    ______________________________________                                        Macro           Manual/PF                                                     Short           Single                                                        Long            Continuous/Focus Tracking                                     ______________________________________                                    

                  TABLE 30                                                        ______________________________________                                        Aperture Value Information                                                    Aperture Value  Focus Mode                                                    ______________________________________                                        Small           Single                                                        Large           Continuous/Focus Tracking                                     ______________________________________                                    

                  TABLE 31                                                        ______________________________________                                        Shutter Speed Information                                                     Shutter Speed   Focus Mode                                                    ______________________________________                                        High Speed      Continuous/Focus tracking                                     Low Speed       Single                                                        ______________________________________                                    

                  TABLE 32                                                        ______________________________________                                        Luminance Information                                                         Luminance       Focus Mode                                                    ______________________________________                                        High Luminance  Continuous/Focus Tracking                                     Low Luminance   Single                                                        ______________________________________                                    

                  TABLE 33                                                        ______________________________________                                        Electronic Flash Information                                                  Electronic Flash                                                                              Focus Mode                                                    ______________________________________                                        Emission        Single                                                        No Emission     Continuous/Focus Tracking                                     ______________________________________                                    

                  TABLE 34                                                        ______________________________________                                        Aberration Information                                                        Differnece Between Axial                                                      And Peripheral    Focus Mode                                                  ______________________________________                                        Large             Manual/PF                                                   Small             Continuous/Focus Tracking                                   ______________________________________                                    

                  TABLE 35                                                        ______________________________________                                        In-Focus Information                                                          In-Focus              Focus Mode                                              ______________________________________                                        During Out Of Focus   Single                                                  After In-Focus        Manual/PF                                               ______________________________________                                    

                  TABLE 36                                                        ______________________________________                                        Detection Propriety Information                                               Propriety         Focus Mode                                                  ______________________________________                                        Possible          Single/Continuous                                           Impossible        Manual/PF                                                   ______________________________________                                    

                  TABLE 37                                                        ______________________________________                                        Object Pattern Information                                                    Contrast       Focus Mode                                                     ______________________________________                                        High           Continuous/Focus Tracking                                      Low            Single                                                         ______________________________________                                    

                  TABLE 38                                                        ______________________________________                                        Defocus Information                                                           Defocus             Focus Mode                                                ______________________________________                                        Small               Single                                                    Large               Continuous                                                ______________________________________                                    

I claim:
 1. A focus detecting apparatus comprising a phototaking opticalsystem for forming an image of an object in a predetermined imagefield;a field detecting device having at least two focus detecting areasand dividing said areas into a plurality of blocks to detect a focus foreach block and to generate a plurality of focus detecting results; adetermining circuit having a plurality of algorithms for determining afocus detecting end result based on the plurality of focus detectingresults, each said algorithm being paired with a focus detecting area; aselecting circuit which selects a paired focus detecting area andalgorithm; and a control circuit which, in accordance with the selectedpaired focus detecting area and algorithm, makes said focus detectingdevice detect a focus with the selected focus detecting area and makessaid determining circuit determine a focus detecting end result with theselected algorithm.
 2. A focus detecting apparatus according to claim 1,wherein said focus detecting device has a first focus detecting areaincluding a center of the image filed and a second focus detecting areawider than that of said first focus detecting area; andsaid determiningcircuit has a center-priority algorithm which gives priority to a focusdetecting result of a block at the center of the image field, and aminimum-focusing-distance-priority algorithm which gives priority to aresult indicating a minimum distance, said first focus detecting areabeing paired with said center-priority algorithm and said second focusdetecting area being paired with said minimum-focusing-distance-priorityalgorithm.
 3. A focus detecting apparatus according to claim 1, furthercomprising:a light metering device having a spot light metering mode formetering light in a narrow area at the center of the image field and awide light metering mode for metering light over the entire image field;and a light metering mode designating member which designates a lightmetering mode, wherein said selecting circuit selects a paired focusdetecting area and algorithm in accordance with a designated lightmetering mode.
 4. A focus detecting apparatus according to claim 1,further comprising:an exposure device which exposes a film to the imageof the object; an exposure controlling circuit which controls saidexposure device to expose properly the film to the image of the object,said exposure controlling circuit having at least two of a time mode forcontrolling a period of an exposure time, an aperture mode forcontrolling a size of a diaphragm aperture of the phototaking opticalsystem, and a program mode for controlling simultaneously the exposuretime and diaphragm aperture; and an exposure mode designating memberwhich designates one of a plurality of exposure modes, wherein saidselecting circuit selects a paired focus detecting area and algorithm inaccordance with a designated exposure mode.
 5. A focus detectingapparatus according to claim 1, further comprising:a release deviceoperable to expose a film to an image formed in an image field; a filmwinding device which winds the film for recording images formed in animage field sequentially, said film winding device having at least asingle winding mode for winding one frame by one operation of saidrelease device and a continuous winding mode for repeating exposures andwindings continuously during operation of said release device; and awinding mode designating member which designates one of said windingmodes, wherein said selecting circuit selects a paired focus detectingarea and algorithm in accordance with a designated winding mode.
 6. Afocus detecting apparatus according to claim 1, further comprising:adriving device which drives said phototaking optical system; a drivecontrolling circuit which controls driving of said phototaking opticalsystem, said drive controlling circuit having at least two of thefollowing five focus modes, (1) a manual focus mode for manually drivingsaid phototaking optical system regardless of focus conditions, (2) apower focus mode for driving said phototaking optical system with saiddriving device regardless of focus conditions, (3) a single focus modefor driving said phototaking optical system to a focus point with saiddriving device in accordance with focus conditions, said single focusmode inhibiting said driving device from driving in accordance withfocus conditions after in-focus is achieved once, (4) a continuous focusmode for always driving said phototaking optical system to a focus pointwith said driving device in accordance with focus conditions, and (5) afocus tracking mode for driving said phototaking optical system to afocus point with said driving device in accordance with a correctedfocus condition which is corrected by adding a quantity corresponding toa movement amount of an object to a detected focus condition; and afocus mode designating member which designates one of said focus modesto make said drive controlling circuit drive-control in the designatedmode, wherein said selecting circuit selects a paired focus detectingarea and algorithm in accordance with a designated focus mode.
 7. Afocus detecting apparatus according to claim 1, further comprising:astrobe device which illuminates an object for photographing; and astrobe mode designating member which designates respective strobe modesthat determine whether or not to illuminate an object with said strobedevice for photographing, wherein said selecting circuit selects apaired focus detecting area and algorithm in accordance with thedesignated strobe mode.
 8. A focus detecting apparatus according toclaim 1, further comprising:a photographing mode designating memberwhich designates a photographing mode including at least two of a lightmetering mode, an exposure mode, a film winding mode, a focus mode and astrobe mode in accordance with an object and photographing conditions,wherein said selecting circuit selects a paired focus detecting area andalgorithm in accordance with the designated photographing mode.
 9. Afocus detecting apparatus comprising:a phototaking optical system forforming an image of an object in a predetermined image field; a focusdetecting device which detects a focus condition of said phototakingoptical system, said focus detecting device having a plurality of focusdetecting areas in different shapes in the image field and dividing saidareas into a plurality of blocks to detect a focus for each block and togenerate a plurality of focus detecting results; a selecting circuitwhich selects one of a plurality of focus detecting areas; and adetermining circuit having a plurality of algorithms for determining afocus detecting end result based on the plurality of focus detectingresults, said determining circuit selecting one of the plurality ofalgorithms in accordance with the selected focus detecting area todetermine the focus detecting end result.
 10. A focus detectingapparatus according to claim 9, wherein said focus detecting device hasa first focus detecting area including a center of the image field and asecond focus detecting area wider than that of said first focusdetecting area; andsaid determining circuit has a center-priorityalgorithm which gives priority to a focus detecting result of a block atthe center of the image field, and a minimum-focusing-distance-priorityalgorithm which gives priority to a result indicating a minimumdistance, said determining circuit selecting the center-priorityalgorithm in accordance with said first focus detecting area andselecting the minimum-focusing-distance-priority algorithm in accordancewith said second focus detecting area.
 11. A focus detecting apparatuscomprising:a phototaking optical system for forming an image of anobject in a predetermined image field; a focus detecting device whichdetects a focus condition of said phototaking optical system, said focusdetecting device having a plurality of focus detecting areas indifferent shapes in the image field and detecting a focus condition ineach area; a release device operable to expose a film to an image formedin an image field; a film winding device which winds the film forrecording images formed in an image field sequentially, said filmwinding device having at least a single winding mode for winding oneframe by one operation of said release device and a continuous windingmode for repeating exposures and windings continuously during operationof said release device; and a winding mode designating member whichdesignates one of said winding modes; and a determining circuit whichdesignates one of the plurality of focus detecting areas in accordancewith the designated winding mode to allow said focus detecting device todetect a focus in the designated area.
 12. A focus detecting apparatuscomprising:a phototaking optical system for forming an image of anobject in a predetermined image field; a focus detecting device whichdetects a focus condition of said phototaking optical system, said focusdetecting device having a plurality of focus detecting areas indifferent shapes in the image field and detecting a focus condition ineach area; a strobe device which illuminates an object forphotographing; and a strobe mode designating member which designatesrespective strobe modes that determine whether or not to illuminate anobject with said strobe device for photographing; and a determiningcircuit which designates one of the plurality of focus detecting areasin accordance with the designated strobe mode to allow said focusdetecting device to detect a focus in the designated area.
 13. A focusdetecting apparatus comprising:a phototaking optical system for formingan image of an object in a predetermined image field; a focus detectingdevice which detects a focus condition of said phototaking opticalsystem, said focus detecting device having a focus detecting area in theimage field and dividing the focus detecting area into a plurality ofblocks to detect a focus in each block to generate a plurality of focusdetecting results; a photographing mode designating member whichdesignates a photographing mode including at least two of a lightmetering mode, an exposure mode, a film winding mode, a focus mode and astrobe mode in accordance with an object and photographing conditions;and a determining circuit having a plurality of algorithms fordetermining a focus detecting end result based on the plurality of focusdetecting results, said determining circuit selecting one of theplurality of algorithms in accordance with the designated photographingmode to determine the focus detecting end result.
 14. A focus detectingapparatus comprising:a photographic optical system for forming an objectimage on an image field; a focus detecting device having a plurality offocus detection blocks arranged in said image field and capable ofgenerating focus signals representing the focus condition of each focusdetection blocks; a selecting circuit which selects one of a pluralityof focus detection areas each focus detecting area including at leasttwo said focus detection blocks; and a calculating circuit having aplurality of algorithms by which a final focus signal is calculated witha plurality of said focus signals and for calculating a final focussignal based on the focus signals of the focus detection blocks includedin the selected focus detection area by one of said algorithms accordingto said selected focus area.
 15. A focus detecting apparatuscomprising:a detecting device which detects a focus condition of a lens,said detecting device including a first detection area covering a firstregion and a second detection area covering a second region smaller thanthe first region, both for detecting the focus condition; a selectingdevice which selects the first detecting area or the second detectingarea based on the photographic magnification of said lens; and acontrolling device which controls said detecting device so as to detectthe focus condition in the first detection area or the second detectionarea selected by said selecting device.
 16. A focus detecting apparatuscomprising:a detecting device which detects a focus condition of a lens,said detecting device including a first detection area covering a firstregion and a second detection area covering a second region smaller thanthe first region, both for detecting the focus condition, both of saidfirst region and second region having an intersection point with anoptical axis of said lens; a generating device which generates anon-axis optical characteristic of said lens and an off-axis opticalcharacteristic of said lens; a selecting device which selects the firstdetection area or the second detection area based on said on-axisoptical characteristic or said off-axis optical characteristic; and acontrolling device which controls said detecting device so as to detectthe focus condition in the first detection area or the second detectionarea selected by said selecting device.
 17. A focus detecting apparatuscomprising:a detecting device which detects a focus condition of a lens,said detecting device including a first detection area covering a firstregion and a second detection area covering a second region smaller thanthe first region, both for detecting the focus condition; a measuringdevice which measures luminance of a scene; a selecting device whichselects the first detection area or the second detection area based onthe measured luminance; and a controlling device which controls saiddetecting device so as to detect the focus condition in the firstdetection area or the second detection area selected by said selectingdevice.
 18. A camera having a focus detecting apparatus comprising:aphotographic optical system which forms an image of an object; anilluminating device which illuminates said object when said object isphotographed by said photographic optical system; an operating memberwhich causes said illuminating device to be operable or not: a detectingdevice which detects a focus condition of said photographic opticalsystem, said detecting device including a first detection area coveringa first region and a second detection area covering a second regionsmaller than the first region, both for detecting the focus condition; aselecting device which selects the first detection area or the seconddetection area based on an operable state of said illuminating device;and a controlling device which controls said detecting device so as todetect the focus condition in the first detection area or the seconddetection area selected by said selecting device.
 19. A camera having afocus detecting apparatus comprising:a photographic optical system whichforms an image of an object; an illuminating device which illuminatessaid object when said object is photographed by said photographicoptical system; an operating member which causes said illuminatingdevice to be operable or not; a detecting device which detects a focuscondition of said photographic optical system, said detecting deviceincluding a plurality of focus detecting areas and generating aplurality of focus signals corresponding said plurality of focusdetecting areas; and a determining device which has a plurality ofalgorithms for determining a final focus detecting result based on saidplurality of focus signals, said determining device selecting one of theplurality of algorithms in accordance with the operable state of saidilluminating device.